2020 GMC Sierra 1500 acceleration problems

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 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 Apr 29, 2026 · Acceleration, Brakes · 80,000 miles · MI

The contact owns a 2020 GMC Sierra 1500. The contact stated that while driving at an undisclosed speed, the vehicle decelerated to 30 MPH. The check engine warning light was illuminated. The vehicle was taken to a local dealer, where it was diagnosed, and determined that the timing belt needed to be replaced. The part was on back order. The vehicle was not repaired. The contact stated the vehicle previously experienced brake failure, sensor failure, and glow plug failure. The manufacturer was contacted, but no assistance was provided. The BBB referred the contact to the federal safety agency Hotline to report the failure. The failure mileage was approximately 80,000.

Filed Mar 23, 2026 · Acceleration, Engine · 70,000 miles · MO

The contact owns a 2020 GMC Sierra 1500. The contact stated that while driving at 65 MPH, the DEF tank failed. The vehicle went into three phases of LIMP Mode and the vehicle unexpectedly decelerated while driving. The DEF system service message was displayed. The vehicle was taken to the local dealer, where it was diagnosed with DEF tank failure, and the tank needed to be replaced, even though the tank was full. The part was on backorder for several weeks. The contact was not provided with a loaner. The vehicle was repaired. The manufacturer was contacted and opened a case, but no additional assistance was provided. The failure mileage was approximately 70,000.

Filed Dec 4, 2024 · Acceleration, Fuel system · LA

Shuttering while in motion at a speed of 35mph or above. My 2020 GMC SIERRA 1500 AT4 CarbonPro while driving at or above speeds of 35mph experiences a hesitation and severe Shuttering while trying to maintain any speed of 35mph or above. The hesitation causes extreme vibrations and hesitation when lifting or applying foot to the accelerator. This happens in any drive mode also with cruise control on or off as well as shifting into low and being in any gear trying to prevent it. It also does this on any road and condition. It feels like a slip in the transmission or torque converter, possibly could be the rear end or variable valve timing as well. And when taking of from a red-light or stop sign it slips as if the truck has lost traction, but it hasn't. This is very dangerous and could be the cause of a serious accident when trying to accelerate. If your traveling at hwy speeds it feels as if the brakes are being applied and the tires are going over a washboard which could cause a collision, tire wear, or driveline damage.

Filed Aug 28, 2024 · Acceleration, Brakes · GA

My brakes failed 2 times. One time I almost got into a horrible wreck with my daughter in the truck. "Brake system failure" " max speed 43mph" I have not had any brake work or anything done. The dealer is trying to charge me to replace the whole brake system when [XXX] this says to reprogram. Still waiting on gmc to tell me if it's covered under warranty. From my own research this has been a major problem for hundreds of people if not more. I could have died because of a faulty brake system or a bad software update. I need help with this and so do the countless other 2020 gm owners. There is a recall on the 2019 for the exact problem but not the 2020s. GM safety recall N192268090 please advise INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Mar 5, 2024 · Acceleration, Electrical · CA

Back window frame crack led to water intrusion which flooded electric module controlling speedometer and adaptive settings. Extremely unsafe driving with faulty electrical components unknown to me. Insurance and Dealership told me this is a common GMC occurrence. Cost is near $10,000 to make truck drivable.

Filed Dec 27, 2022 · Acceleration, Brakes · CA

i was stopped at a red light and when the light turned green I accelerated and the vehicle shut off and then came back on. when the vehicle came on i had a service esc light and a system break failure warning telling me not to exceed 62mph. i made it back to my house driving with extreme caution. the breaks were very delayed while driving.

Filed Jul 9, 2022 · Acceleration, Brakes · AR

The truck stated to have the check engine light on, by the time that happened the brakes were hard to step on it and the steering wheel hard to turn, I had been asking to GMC superior of Siloam springs to check the truck because, got scared while I couldn't make stop the truck while on traffic, but they don't had open appointments for that day or the other following days, so a week after they got one and I missed because my work, I set another one at GMC on Springdale but they want me to charge me whenever the truck has an extended warranty, so I told them to leave it like that so finally got another appointment at Siloam springs location but while driving down there the same thing happened all the light on warning messages on the dash board start showing up and the brakes were hard to step on it and the steering wheel hard to turn, I got told them what was happening, about and how exactly happened. That day after 30 minutes I got a call saying that it was fixed I still asked if they were sure he said yes, the next day I almost crashed with a neighbor at my work place because I couldn't stop the truck, so today I took back the truck and the guy at the desk told me that they may just erase the codes and don't really checked what was wrong, I'm just filling this report because even if I got full coverage on that truck, I'm not gonna be responsible if I'm involved in an accident.

Filed Jun 16, 2022 · Acceleration · FL · crash · fire · 7 injuries

I investigated and Unintended Acceleration crash that occurred on 8-9-2021. The vehicle had just left a body shop where it had repairs to the left front of the vehicle near the ECM. The driver reported the vehicle would not slow down. He face timed a witness and showed her his foot was on the brake and not the accelerator pedal collaborating his statement. The 2020 GMC accelerated to 93 miles per hour crashing into the back of a Cadillac Escalade. Upon impact the fuel tank of the Cadillac exploded igniting both vehicles on fire and burning a fed-x truck that was folded in half from the sever impact. The EDR report stated the brakes were applied fully for a full 5 seconds prior to the crash while the vehicle was still accelerating. The accelerator was reading a constant 57% during the lead up to the crash and the brake rotors showed heat related glazing from excessive braking. The engine torque was also at 1023NM leading up to impact collaborating Unintended Acceleration further. Based on the evidence gathered my opinion is there was a short in the components in the left front of the vehicle most likely the ECM harness that caused the crash. It is unknown if the damage was caused by the previous crash, the body repairs or a manufacture defect at this time. The radiator had also just been replaced so moisture could have contributed to the malfunction. If moisture shorts APP-1 to APP-2 the safety systems can fail to detect a single fault because it causes redundant faults