2020 GMC Sierra 3500 Powertrain (other) Problems

My truck has been exhibiting hard downshifting at certain speeds, when the powertrain loads up such as a grade change, and requires a downshift. I have complained about this issue to the dealership as early as 2022, and 33,185 miles. The dealership made me pay for a transmission $388.90 flush which did not resolve the issue. The problem has become progressively worse, to the point where the toll road transponder fell of my windshield during a recent harsh downshifting incident. At the same time there was an existing MIL and derating for a DEF heater and NOx sensor failure, so during a warranty visit I asked that this transmission issue be addressed. On Friday March 13, the dealership called and said they confirmed the hard downshifting, albeit not as extreme as I described. The technician said that the valvebody needs to be replaced. At the same time, they performed a TCM flash for the 10L1000 momentary wheel lockup recall. The dealership then said they could not get the truck to set a P0747 code, said that GM refuses to replace the faulty valve body, and recommended I take the vehicle home unrepaired, and to come back when the P0747 code is set. I requested they continue to drive the vehicle. Today March 20 the dealership called and said they could not get the code to set, and that I need to drive the truck and come back when the code appears, despite the truck exhibiting clear symptoms of a progressively wearing feed limit low valve. N242454441 does NOT seem to indicate a P0747 code is required to replace the valve body. This vehicle is not safe for towing a 20,000+lbs and GMC is refusing to repair a transmission with symptoms congruent with N242454441. The dealership still has possession of the vehicle and wants $360+ in diagnostic labor.

NHTSA ID

11725965

Incident

Mar 12, 2026

The contact owns a 2020 GMC Sierra 3500. The contact stated that while driving at an undisclosed speed, the vehicle inadvertently went into LIMP Mode. There was no warning light illuminated. The vehicle was taken to the dealer, where it was diagnosed that the transmission valve body sensor had failed and needed to be replaced. The vehicle was not repaired. The manufacturer was made aware of the failure and referred the contact to the NHTSA Hotline for assistance. The approximate failure mileage was 130,000.

NHTSA ID

11672242

Incident

Jul 9, 2025

Mileage

130,000 mi

The contact owns a 2020 GMC Sierra 3500. The contact stated that while driving at 60 MPH, the rear differential seized, in addition, the contact was hauling a median size tracker on top of a flat bed. The flat bed jackknifed and hit the left side of the contact's vehicle. The vehicle was able to come to a stop. The air bags did not deploy. There was no warning light illuminated. A police report was filed. There were no injuries sustained. The vehicle was towed to a towing yard. The trailer was towed to the residence. The tractor was damaged in the accident. The vehicle was diagnosed by an independent mechanic. The contact was informed that the transmission had failed. The vehicle was not repaired. The insurance company was contacted. A claim was filed with the insurance company, and it was canceled a few days later by the insurance company. The manufacturer was not notified of the failure. The failure mileage was approximately 108,000.

NHTSA ID

11672009

Incident

Oct 2, 2024

Mileage

108,000 mi

Valve body failed while pulling my camper down the interstate. Transmission began to have issues and locked up on us while driving. Luckily i was able to avoid any accidents. Had truck towed to a private Transmission shop to have the transmission repaired. Shop advised the failure was due to the faulty valve body.

NHTSA ID

11654874

Incident

Feb 9, 2025

Greetings. In December 2024, I brought my vehicle in for the rear end lock up recall. The recall reprogrammed the transmission control module. As admitted, by yourself and GM this doesn't fix the problem. In addition, if the lockup occurs and a new valve body is required, GM is on back order with no date for delivery. Also, it is replacing it with the same valve body, i.e. you will have the same problem in the future. Nextgen Drivetrain has a valve body for around $1000 that fixes the problem. [XXX] . Please read the attached blog from Nextgen, they explain in detail, the problems and the fixes. I am scared to death to pull my travel trailer out of state with this looming problem. Please give us a better solution. Thank you. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

NHTSA ID

11648300

Incident

Dec 10, 2024

The contact owns a 2020 GMC Sierra 3500. The contact received notification of NHTSA Campaign Number: 24V797000 (Power Train); however, the part to do the recall repair was not yet available. The contact was concerned about the remedy repair not being adequate to repair the vehicle. The local dealer was contacted. The contact stated that the manufacturer had exceeded a reasonable amount of time for the recall repair. The manufacturer was made aware of the issue. The contact had not experienced a failure. Parts distribution disconnect.

NHTSA ID

11646537

Incident

Mar 5, 2025

Engine Coolant Low error constantly appears. GM Service provider states that engine coolant level is fine, but sensor may be defective.

NHTSA ID

11639548

Incident

May 12, 2023

Contacted General Motors to have the Recall software patch installed, appoint was set, vehicle was dropped off and now they are telling me there is nothing they can do, that the recall is not available. The software update is available, and is being installed on other vehicles. This is a life safety issue as the rear wheels can lock up at any time which could cause a vehicle accident involving the vehicle under recall as well any vehicles on the road around this vehicle when it happens. General Motors should be taking care of this asap instead of waiting. I do not feel safe driving the vehicle until they feel like they installing it.

NHTSA ID

11634795

Incident

Oct 24, 2024

I have a complaint about the recall response from both nasal and gm. I feel the cure is substandard. Why not just put new transmission control modules in to correct this problem. Very disappointed

NHTSA ID

11626032

Incident

Nov 2, 2024

driving 65mph on interstate, attempted to change lanes to pass slower vehicle and pressed upon accelerator pedal...truck violently skidded to a stop and sent me onto shoulder, many vehicles behind me swerved to avoid my vehicle. GM wont repair and says since they cant replicate its not really happening. this has happened twice in last 2 weeks.

NHTSA ID

11602485

Incident

Jul 15, 2024

driving approximately 50 mph when vehicle suddenly made loud bang and locked up rear brakes for 25' coming to a stop in road side ditch, numerous vehicles had to make evasive actions to avoid me and other vehicles. flat spotted tire abut no visible physical damage. sat on side of road for transmission temp to cool down then drove to shop without repeat. called dealer was told the earliest appt was a month away. have not been able to repeat incident so far. this has happened a few times and is becoming more frequent, mfg has tsb issued but indicates they cant assist because my warranty has expired so i will have to pay 225 per hour diagnostic fee. this is untenable and dangerous. this needs a recall and repair ASAP.

NHTSA ID

11598428

Incident

Jul 1, 2024

driving 45 mph westbound i70 at eisenhower tunnel, vefhicle made loud bang, brakes locked up momentarily slowing vehicle to around 25mph. multiple vehicles had to make evasive manuevers to avoid collision. vehicle released after a 15FT skid. pulled over to safety and inspect for damage, tires were falt spotted but no damage was visible. called dealer servcei and was told to make appt and set for diagnostic. service could not replicate or find damage so I was sent on my way and told if it does it again let us know. I am scared to drive this vehicle its unsafe

NHTSA ID

11598426

Incident

Mar 30, 2024

driving 65mph when vehicle attempted to downshift itself for no reason when instead the rear axles locked up and made a massively loud bang as if axle fell off, let off gas, smoke pouring from rear tires, skidded about 8 feet, it released then locked up 2 more times within 30 secs before I could get off road out of traffic flow. mfd has a tsb for this issue(#21-NA-275 GM) not sure if its transmission or braking system Dealer service could not replicate and told me it was probably my trailer(wasnt traveling with trailer) no warnings, no codes occurred initially at 56000 mile, has happened 10 or 12 times since then. very scary, im afraid to drive or tow now that dealer mentioned trailer brakes.

NHTSA ID

11598370

Incident

Jul 1, 2024

I was driving approximately 60mph pulling a trailer when the back tires locked up for approximately 2 seconds. This happened 3 times within 30 minutes. I've taken it to the GM repair shop. They have seen this happen to 3 or 4 vehicles. Due to not being able to replicate the fault it has been difficult to diagnose. They are going to replace the transmission valve body hoping that will take care of the issue. This is extremely dangerous to everyone on the road when this happens. There are many forums out there that I've read and have been close to deadly accidents involving cars, trucks, RV's, and semis as they've ran off the roads. This seems to be something worth looking into and ensuring GM puts out a recall for. In my case, I am going through an extended warrant for my 2020 3500 with 112,000 miles. The warranty company wants the GM technician to replicate the fault... which isn't possible without hooking up a trailer... also very dangerous which I refuse to do until the issue if resolved. In any case, I will have to hook up a trailer once the part is replaced... praying that it won't happen again.

NHTSA ID

11585881

Incident

Apr 7, 2024

The contact owns a 2020 GMC Sierra 3500. The contact stated that after stopping at a stop light, the light turned green and the contact depressed the accelerator pedal however, the vehicle failed to accelerate as intended. The contact drove a short distance and noticed that the failure was reoccurring. The contact drove the vehicle to a safe location and turned off the vehicle. The contact exited the vehicle and noticed that the exterior of the vehicle was covered with transmission fluid. The contact stated that the transmission fluid was also on the undercarriage of the vehicle and on the ground. The vehicle was towed to the dealer where it was diagnosed with a failed transmission fluid line. The contact was informed that the transmission fluid line needed to be replaced. The vehicle was not repaired. The manufacturer was made aware of the failure and advised the contact to report the failure to the NHTSA Hotline. The failure mileage was approximately 28,000.

NHTSA ID

11559106

Incident

Dec 1, 2023

Mileage

28,000 mi

While accelerating from about 45 - 60mph the truck made a loud bag and the rear tires locked up causing the vehicle to skid. This happened 4 times and nearly caused the cars behind me to crash.

NHTSA ID

11530042

Incident

Jun 24, 2022

Rear tires locking up out of no where almost made me jack knife.

NHTSA ID

11501953

Incident

Jan 15, 2023

The exhaust system is directed to the rear of the vehicle and when towing causes extreme heat to build on the item being towed, in my case a 5th wheel camper. The heat has melted the trim on my camper and is a potential fire hazard.

NHTSA ID

11485406

Incident

Sep 12, 2022

The computer lite up the dash and reduced power, plus took the trailer brakes off line. This happened while loaded. To reset the system you have to pull over and turn the vehicle off. This happens 2-3 times per day. This was a problem at 600 miles. The transmission shifted from 10 gear to 5th gear while driving 75 miles per hour. The truck had 75,000 miles on it . Had to send another truck out to pick up the load in Santa Rosa New Mexico. The dealer Glenn Polk in Sanger has been working on for the last 4 months There is never a warning until the lights come on with a system failure.

NHTSA ID

11418595

Incident

May 1, 2020