2020 GMC Sierra 1500 transmission problems

Filed Oct 23, 2026 · Engine, Transmission · WI

I own a 2020 GMC sierra AT4. It has developed a shudder when cruising on the highway or driving in town around 1500rpm. I believe it is coming from the transmission. A local shop mentioned the torque converter. The shudder feels like a delay in power and makes it difficult to hold speed or accelerate when needed.

Filed Oct 17, 2026 · Engine, Fuel system · NY

[XXX] General Motors Company P.O. Box 33170 Detroit, MI 48232-5170 c/o Franklin, Customer Support Re: Formal Demand for Buyback – 2020 GMC Sierra AT4 Black Widow VIN: [XXX] | 6.2L Engine Recall ~ 25V‑274. Plus ~ GM 10-Speed Transmission, Multiple Recalls Dear GMC Legal, I am providing written notice as required by 15 U.S.C. §2310 and New York State Lemon Law. This vehicle substantially impairs the safety, use, and value of my truck, and I am requesting a full buyback. The Facts: On [XXX], the vehicle was taken out of service and remained at the shop for 11 weeks. It was returned with yellow marking paint splattered on the exterior, floor mats, and brake pedal. On [XXX] — with fewer than 400 miles on the replacement engine — the engine and/or transmission suddenly shut off at 55 mph on [XXX]. It restarted with a violent boom, then cycled between shutting off and restarting with loud clacking and shaking for the remainder of the drive. I was forced to drive at 25 mph with hazard lights to reach home. The Legal Basis: This is a safety defect on a vehicle subject to Recall 25V‑274. GM was on notice of this known, concealed defect. The vehicle has been out of service for 30+ cumulative days. I have been denied a reasonable opportunity to cure. The vehicle has caused me severe and ongoing psychological distress, imminent and uncontrolled danger to my life, and total and continuing loss of use for its fundamental purpose. My Demand: 1.Full buyback under New York State Lemon Law — full purchase price, loan payoff, taxes, registration, and all incidental and consequential damages. 2.$5,000 additional compensation for the safety hazard and loss of use. 3.Attorney's fees and costs under 15 U.S.C. §2310(d)(2). I reserve all rights under the Magnuson-Moss Warranty Act, New York State Lemon Law, and all applicable consumer protection statutes. Please respond in writing within 10 business days. If unresolved, I will join the c INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Sep 28, 2026 · Acceleration, Transmission · MS

The vehicle in questions was purchased with less than 5 miles in year 2020. This vehicle was dropped off at MAC HAIK CHEVOLET MADISON MS on September 25, 2026. I was advised on September 28, 2026, that the vehicle was test driven with the scan tool connected, Graph Torque converter slip, found over 100 RPM slip when torque converter engaged and causing shutter at highway speeds, also felt 1-2 and 2-1 harsh downshift, check fluid condition was black and smelled burnt, replace transmission assembly, flush cooler, program transmission control module and perform clutch fast learn. Estimated cost of $8k

Filed Sep 15, 2026 · Electrical, Engine · MS

5/5/25 woke up back seat entire truck flooring soaking wet back glass cracked. 4/8/25 transmission went out 117,000 miles 7/3/25 exhaust leak and placed nox 1. 7/8/25 127551 mileage exhaust leak replace gaskets, belt , tensioner, and pulley, 6/8/2025 3 knock sensors replaced and replaced intake manifold.

Filed Sep 14, 2026 · Transmission · AR

Transmission shifting hard in first few gears and only 87,000 miles on Transmission.

Filed Sep 9, 2026 · Engine, Transmission · TX

Powertrain issues and a chassis issue that is extremely dangerous.Tailgate on rare occasions falls open by itself. There is a design flaw in the placement of the catalytic converters. The heat is burning up the fluid. I could not believe my eyes when I serviced the transmission. This is another shortcut by GM to save on the extra wiring needed for the oxygen sensors (2)in the converters and the two oxygen sensors downstream of the converters. There is plenty of room for the converters further down by the tail shaft to drive shaft connections. This is GM’s way of being cheap. Here’s the problem. The converters get way too hot. The fill plug for the transmission which is behind a low rent heat shield crumbled into my hands from excessive heat buildup. GM knows there is a problem with the fluid breaking down. Their bandaid answer is to use Mobil 1 fluid instead of the recommended Dexron 6. What needs to happen is a safety recall issued for the unwanted tailgate deploying all by itself. There needs to be a redesign in the exhaust system. The Transmission (8 Speed) has a catalytic converter exactly on both sides and the crossover pipe runs directly under the transmission sump pan. No wonder they are having issues with transmissions burning up. THIS IS A FIRE HAZARD !!! With the converters being so close to the exhaust manifolds, a leak from the engine or the transmission would be enough to ignite and possibly kill the occupants. All in the name of saving a few cents in wiring. Myself, I am a retired GM Mechanic. I started working at Sewell Cadillac in [XXX] in 1975. I have held the title of ASE Master Tech. Cadillac Master Tech. I have been a GM Shop Foreman and A GM Service and Parts Director in my Career. I retired from Federal Express as in charge of Fleet Maintenance and GSE(Aircraft Equipment). I have certifications from Mercedes, BMW, Toyota, Commander Loaders, Goodyear, and more. Given the right set of circumstances, it could end very badly. Dangerous Truck ! INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INF

Filed Aug 26, 2026 · Acceleration, Transmission · AR

This truck was bought brand new by my father. Around 38,000 miles it begin having issues with shifting which eventually got worse. When I searched google for issues many others on different pages have had the same issues. The shifting would be so rough it feels like you're being hit by another vehicle. This could cause accidents for anyone who cannot afford to fix these known issues by GMC. I was told today by my local dealership their transmissions for my specific truck is on backorder. Should that not indicate an issue when this truck is a 2020. But to my father having a stroke I was not able to handle this issue sooner as he was very ill for four years and passed last year. The truck was not the priority at the time.

Filed Aug 26, 2026 · Engine, Transmission · NY

High pressure fuel pump went at 80k and now on my 2nd transmission under 100k miles this is absolutely absurd

Filed Aug 24, 2026 · Engine, Transmission · GA

The 5.3L Engine active fuel management failure problem. This known problem with the GMC motors was not disclosed by any dealerships or the manufacturer. While driving down the roadway, the truck had an engine malfunction and I was fortunate enough to be able to safely pull over. The check engine light activated and I took it to the dealer the next day. I was informed by the dealer that this was a known, common issue that GM was aware of but was not offering assistance. I had to pay $11,000 out-of-pocket because of this.

Filed Aug 24, 2026 · Electrical, Engine · TX

Our 2020 GMC SIERRA 1500 has suffered catastrophic systems and engine failure including the brakes multiple times for almost 4 years. It has happened in high traffic and on the interstate each time having to be coasted off of the road to come to a rolling stop. There have been nine repair attempts with GM dealers repeatedly stating the issues were repaired and returning our vehicle to us. We began making the CEO and Executive team aware of the potentially deadly safety hazards including the fact that I, [XXX] am disabled and power wheelchair dependent requiring a truck that can carry my power wheelchair. We have sent numerous emails to Ms. [XXX] and the Executive team numerous times informing them in detail, each time, of all issues involved. We started communicating via phone and email with customer care to no avail. All attempts at repair finally ended in complete engine failure leaving us with an estimate to replace the engine of over $13,000. We have also, submitted a detailed complaint to the Attorney General’s Office and after review were given the Case # TCP - XXX. I will attach the Complaint and Addendum sent to the Attorney General along with two of the emails sent to Ms. [XXX] and her team informing her of all issues with the truck. They took no action to actually help us get this truck off of the road knowing it was having catastrophic engine and system failure and that it had to be driven to transport a disabled power wheel dependent with severe medical issues and the medically necessary power wheelchair. I am also attaching the earliest OnStar Diagnostic notice of Engine, Transmission and Emissions system issues from May of 2023. The issues have remained the same from the beginning only worsening though my husband has only driven the truck in town on slower less busy streets learning how to make adjustments such as pumping the brakes and starting and stopping the truck to keep it going. My carrier is installed and yet it is undrivable. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATIO