Stop the 8-Speed Shudder: What Your Dealer Won’t Tell You
Quick Answer
The primary issue with the 2017-2020 Silverado’s 8L90 8-speed transmission is harsh shifting, shuddering during acceleration, and torque converter failure. The shudder is often caused by degraded transmission fluid that fails with heat.
Approximate Cost: A full fluid flush with the correct GM-specified fluid (GM Part # 19417577) runs $350-$500. A torque converter replacement, a common repair, typically costs $2,800-$3,800.
Time to Fix: A fluid flush takes about 2 hours. Replacing the torque converter is a major job requiring 8-12 hours of labor.
Actionable Advice: If you experience shudder, have the transmission fluid flushed immediately with the updated Mobil 1 HP fluid to potentially avoid a much more expensive converter replacement.
For specific year variations and engine codes, see the detailed sections below.
Overview
The 8L90 eight-speed automatic transmission, used in the 2017-2020 Chevrolet Silverado and GMC Sierra 1500 trucks with certain V8 engines, is a high-performance unit designed for improved fuel economy and shift performance. However, it has been the subject of widespread customer complaints and technical service bulletins (TSBs) for issues related to harsh shifting, shuddering, and premature wear.
Common symptoms include a pronounced shudder or vibration during light acceleration (often felt between 25-45 mph), harsh or clunky 1-2 and 2-1 shifts, and delayed engagements. The root cause is frequently traced to the torque converter and degraded transmission fluid. GM released updated fluid specifications (Dexron HP ATF) and multiple TSBs, including TSB #18-NA-355 and TSB #19-NA-219, which outline a flush-and-fill procedure with the new fluid and, in many cases, require torque converter replacement.
A standard repair for the shudder under these TSBs involves a complete transmission fluid exchange (approximately 14 quarts of Dexron HP, GM part number 19417577) and a torque converter replacement (part number 86806367 is common). This repair typically books around 6.5 to 8.0 hours of labor. Parts and fluid can cost between $1,200 and $1,800, with total repair bills often ranging from $2,500 to $3,500+ at a dealership. It is a significant but common fix for this specific model range.
Symptoms
Common Symptoms: 2017-2020 Silverado/Sierra 1500 with 8L90 8-Speed Transmission
These symptoms are specific to the GM 8L90 (M5U/M5X RPO code) 8-speed automatic transmission. Issues often relate to the torque converter, fluid aeration, and control system calibration.
- Hard 1-2 or 2-3 Upshifts: Feels like a firm “clunk” or “bang,” especially when cold. This is often the primary driver complaint and is frequently linked to a faulty torque converter clutch apply circuit.
- Shudder or Vibration Under Light Acceleration: A rhythmic shaking felt through the seat and steering wheel, typically between 35-55 MPH. This is a classic sign of torque converter clutch (TCC) shudder caused by degraded fluid or a failing converter (GM Part # 86835667 for updated unit).
- Harsh/Delayed Reverse Engagement: Significant “clunk” and lurch when shifting into Reverse, often with a 1-2 second delay. Points to issues with the low/reverse clutch circuit or main control valve body.
- Erratic Shifting or “Hunting” for Gears: Transmission seems confused, randomly upshifting and downshifting on the highway. Commonly caused by faulty pressure switch manifold or solenoid issues, requiring replacement of the main control assembly (GM Part # 86835645).
- Loss of Propulsion or Neutral-Out: Engine revs but vehicle does not accelerate, as if shifted into Neutral. This is a serious symptom often related to pump failure, severe clutch wear, or internal pressure loss.
- Transmission Overheating Warning on DIC: Message displays “Service Transmission” or “Transmission Hot Idle Engine.” Frequently traced to a failing thermal bypass valve in the cooler circuit, which should be replaced with an updated part (GM Part # 86774933).
- Fluid Leak from Bellhousing Area: Indicates a leaking torque converter seal or front pump seal. This can lead to low fluid levels, which exacerbates all other shifting problems.
Note: A critical first step for most of these symptoms is performing a transmission fluid flush using Mobil 1 LV ATF HP (GM Part # 19417577) and updating the Transmission Control Module (TCM) software to the latest calibration. Many early concerns were addressed by technical service bulletins (TSBs).
Diagnosis
Diagnostic Guide: 2017-2020 Silverado/Sierra 1500 8L90 & Related 6-Speed Transmissions
Authoritative Note: The core issue for these model years is the GM 8-speed 8L90 transmission (RPO code M5U). The 6L80 and 6L90 are different, older 6-speed units but share some diagnostic principles. This guide focuses on the prevalent 8L90 concerns.
- Identify the Complaint & Transmission Type
First, confirm the transmission RPO code on the glove box label. For 2017-2020 trucks with the 5.3L or 6.2L V8, the problematic unit is typically the 8L90 (M5U). Common complaints include:
- Hard 1-2 or 2-3 upshifts, especially when cold.
- Clunky or harsh downshifts when coming to a stop.
- Shudder or vibration during light acceleration (often mistaken for a torque converter issue).
- Scan for Codes & Check TCM Software
Connect a capable scan tool (GDS2 is ideal). Check for any transmission-related DTCs (e.g., P0700, P0711-P0712, P0961). The most critical step is to check the Transmission Control Module (TCM) calibration. GM released multiple updated software flashes to address shift quality. A reflash is often the first and most cost-effective fix (approx. 1.0 labor hour, ~$150 dealer fee).
- Perform a Fluid Inspection & Flush
If the shudder is present, the primary culprit is fluid breakdown. The original Dexron HP fluid is hygroscopic and shear-sensitive. Drain the fluid and inspect. A burnt smell or metallic debris indicates internal damage. The prescribed fix is a complete triple flush using the newer GM Mobil 1 HP LV ATF (GM Part # 19417577). Parts & fluid cost: ~$300-$400. Labor: 2.5-3.0 hours.
- Diagnose Torque Converter & Clutch Operation
If shudder persists after a proper flush, the torque converter clutch is likely damaged. Monitor TCC slip RPM and pressure control solenoid data in GDS2. A confirmed faulty torque converter requires transmission removal. Part cost for a remanufactured converter (GM Part # 84629745 for many applications) is ~$500-$700. Labor for R&R transmission: 8.0-10.0 hours.
- Internal Valve Body & Pump Assembly Inspection
For persistent harsh shifts, the valve body or control solenoid assembly may be at fault. Check for stuck valves or solenoid failures. A common repair is replacing the main control assembly (GM Part # 86774933 – varies by model year). Part cost: ~$450-$600. Labor for drop-pan replacement: 2.0-3.0 hours.
- Complete Overhaul or Replacement
If internal damage is found (e.g., burnt clutches, planetary failure), a remanufactured transmission is the most reliable path. A GM Remanufactured 8L90 unit (GM Part # 86819124 – example) can cost ~$3,200-$3,800. Total job cost with labor (12.0-15.0 hours) and fluids often exceeds $5,500.
Final Recommendation: Always start with diagnostics and a software update. For shudder, the fluid flush is step one. Avoid aftermarket “fix-in-a-bottle” additives. Use only the specified GM HP LV fluid for the 8L90.
Fix
The shudder and harsh shift issues on the 2017-2020 Silverado/Sierra with the 8L90 (and related 6L80/6L90) are well-documented. The permanent fix involves a multi-step procedure, not just a fluid change. Here is the approved repair process:
- Diagnostic Verification
Confirm the concern with a road test, focusing on torque converter clutch (TCC) shudder between 35-80 mph. Use a scan tool to monitor TCC slip speed; a cyclic variation of +/- 20 RPM indicates shudder. - Perform Triple Flush Procedure
You must completely exchange the old Dexron HP fluid. This requires a flush machine or multiple pan drops. Simply dropping the pan once only changes about 40% of the fluid. The new fluid is critical. - Refill with Updated Fluid
Use GM-approved Mobil 1 Synthetic LV ATF HP (Part # 19417577) only. Do not use the old Dexron HP fluid. The new fluid has revised friction modifiers. You will need approximately 12-14 quarts for a full exchange. Cost for fluid: ~$12-$15/quart. - Relearn Transmission Adaptive Functions
Using a professional scan tool (like GM GDS2 or a capable aftermarket tool), perform the TCM Reset/Relearn procedure. This clears the old adaptive shift tables, which are calibrated to the old, degraded fluid. This step is mandatory for the fix to work. - Road Test for Re-Adaptation
Drive the vehicle through a specific learn cycle: multiple gentle stops, part-throttle acceleration, and bringing the transmission through all gears. This allows the TCM to rebuild its adaptive tables with the new fluid.
If the Shudder Returns: If the shudder returns after this procedure, the torque converter is likely damaged and requires replacement. The approved converter for this repair is often GM Part # 86806367. Converter replacement labor is typically 8.0-9.0 hours, plus the cost of the converter (~$500-$700) and another full fluid exchange.
Important Note: Some 2019-2020 models may have a serviceable transmission fluid filter (Part # 24267339). If equipped, replace this filter during the fluid exchange. Earlier models have a non-serviceable internal filter.
🔥 Need the Complete Picture?
We’ve compiled every tick, shudder, and warning light for every Silverado year into one massive, 15,000-word master guide.
Real Owner Discussions
“Got a ’20 Silverado 1500 with about 75k on the clock. The damn thing just revs to the moon like it’s free, but it won’t pull the skin off a rice pudding. Feels like the tranny’s taking a nap. Gonna throw some Mobil 1 juice at it and see if it wakes up before it grenades.”
“My ’15 Chevy’s a garage queen with only 50k on the clock, and the damn torque converter’s already shaking the whole truck apart. Gonna try that thermal bypass band-aid before the whole tranny grenades.”
“My ’19 with only 45k on the clock is acting like a total dog. The tach is dancing but the damn thing’s just loafing along, feels like the tranny’s taking a nap. Unreal I dropped fifty large at the stealership for this paperweight.”
*Real discussions sourced from Silverado owners online.
❓ Frequently Asked Questions
2018 Silverado 8-Speed (8L90) Transmission FAQs
1. What are the most common symptoms of a failing 8L90 transmission in my 2018 Silverado?
The most reported issues are harsh 1-2 and 2-3 upshifts, shuddering or vibration during light acceleration (often feels like driving over rumble strips), delayed engagement into Drive or Reverse, and erratic shifting. The shudder is frequently misdiagnosed as a torque converter issue but is often related to the transmission fluid and clutch apply calibration.
2. Is there a factory fix or Technical Service Bulletin (TSB) for the shudder problem?
Yes. GM released TSB #18-NA-355 (updated by #19-NA-219) specifically for the 8-speed shudder. The official fix is a complete triple-flush of the transmission fluid, replacing the old Dexron HP fluid with the new GM Mobil 1 Synthetic LV ATF HP (GM Part # 19417577). The bulletin also requires a transmission control module (TCM) recalibration. The fluid itself is about $18-$22 per quart, and the job typically takes 3.0-4.0 labor hours.
3. Will a simple fluid change fix my shuddering transmission?
Usually not. A standard drain-and-fill only replaces about 5 quarts of the total ~11-quart system. The TSB-mandated triple-flush process is critical because it uses a transmission flush machine to exchange nearly 100% of the old, degraded fluid. This, combined with the TCM reflash, addresses the fluid’s frictional properties and the clutch control strategy together.
4. My truck is jerking harshly between gears. Could it be the torque converter?
Absolutely. The 8L90’s torque converter clutch (TCC) is aggressively applied for fuel economy and is a common failure point. A faulty converter can cause shudder, slippage, and harsh engagements. Diagnosis requires a professional scan tool to monitor TCC slip data. A replacement GM torque converter (Part # 86806367 for many 2018 models) costs $450-$650 for the part, with total repair labor around 8.0-10.0 hours (requires transmission removal).
5. Are there any known valve body or solenoid issues with the 8L90?
Yes. Issues with the main control valve body (also called the control solenoid valve assembly) are common and cause delayed shifts, harsh shifts, and loss of gears. GM has released updated parts. A new valve body assembly (GM Part # 86846333 is a common update) costs $550-$750. Replacement labor is significant, often 5.0-6.0 hours, as it involves dropping the transmission pan and performing critical relearn procedures with a GM scan tool.
Note: The 6L80 and 6L90 are different 6-speed transmissions. This FAQ focuses specifically on the 8-speed 8L90 found in 2017-2020 Silverado/Sierra 1500 trucks with the 5.3L and 6.2L V8 engines.
🔗 Related Silverado Guides
🔧 Official GM Resources
Check Recalls
Owner Manuals
GM Parts
Service Bulletins
Legal & Financial Disclaimer
Not Professional Advice: SilveradoFix.com content is for informational and educational purposes only. We are not providing professional mechanical, legal, or financial advice. Always consult a certified mechanic before attempting any repairs.
Cost Estimates: All prices, part costs, and labor times are 2026 estimates based on market research and owner reports. Actual costs vary significantly by location, shop rates, and vehicle condition.
No Liability: By using this information, you agree that SilveradoFix.com, its owners, authors, and affiliates are not liable for any damages, injuries, losses, or costs resulting from the use or misuse of this information.
Independent Site: SilveradoFix.com is an independent online resource and is NOT affiliated with General Motors, Chevrolet, GMC, or any of their subsidiaries.
Emissions Warning: Modifications like AFM/DOD deletes may affect emissions system compliance and could be illegal in some states. Check local regulations.