2023 GMC Sierra 2500 AT4 with approximately 36,000 miles as of current. The vehicle has experienced three valve body failures to date. GMC dealerships have completed one GM remanufactured transmission replacement and an overhaul of the second transmission. The third valve body has now failed. A GMC transmission specialist confirmed transmission failure upon recent test drive on 2/24/2025. GMC dealership refuses to perform warranty repair as they are stating -??a recall is being developed-?? therefore will not repair/replace current defective powertrain parts. I was given the vehicle back with the verbal disclaimer -??it should be safe to drive but the rear wheels can lock up at highway speed so be aware.-?? The failure causes extreme harsh downshifting and what feels like a momentary rear wheel lock up. I have experienced this numerous times at lower speeds (<40mph). The check engine light does not come on.

- Northwood, OH, USA

As I was driving on a paved public road, my truck shifted up/down multiple times on it's own in quick succession, then jerked the truck forward. The check engine light came on and the driver information center displayed 'Engine power reduced'. I had to return to my home which was closer than a dealer for service. I'm fortunate that this didn't happen while towing as I regularly do or while I'm on the freeway which I use several times a week. There was no warning that this was going to happen (e.g., no indicator lights or messages or even strange behavior from the vehicle). The GMC dealer confirmed the valve body in the transmission needs to be replaced and the part is on backorder with no ETA.

- Tucson, AZ, USA

I was driving on the interstate and had just exited to refuel. As I was re-entering traffic, I accelerated to merge, and suddenly, as I was about to pull in, I felt and heard a massive metallic crash, like the entire transmission had dropped. The engine sounded abnormal, and immediately, the dashboard flashed a warning: 'Engine Power is Reduced.' The check engine light came on, and I got messages saying the transmission needed service and to schedule an appointment. I called my dealership and took it in as soon as possible. After they held the truck for a while, the service manager told me a critical part was on indefinite backorder with no fulfillment date. He handed back my keys, saying they'd reach out when it arrived. I asked if it was safe to drive, and he said yes. Later, driving from Illinois to California, my truck malfunctioned again. This time, in heavy, 12-lane traffic, the same loud crash threw me forward, almost slamming my face into the steering wheel. My wrists and shoulders hurt from bracing myself, and my right shoulder still aches. Again, I got the 'Engine Power Reduced' warning and transmission service notice. Each time, this has put me and those around me in severe danger.

- Marion, IL, USA

2023 GMC Sierra Duramax Diesel with 10 speed Allison Transmission with 28,000 miles can't be driven. Currently at the dealership due to a transmission valve body problem, codes P0700 & P0747. While driving I felt a hard shift and the truck jerk. The engine light came on and my truck went into low power mode. Let it sit over night and truck would shift fine. This happened 3 times over a 1 month period. After getting to the Chevy dealer they told me the issue is with he valve body and said they have been having multiple trucks come in with the same problem. They have a truck in there since May (4 months!) They told me there is no ETA for the part. I've read this is a common issue happening on 2023 & 2024 trucks like mine. I've read that the problems have been going on for over 1 year. This is ridiculous for a $90,000 truck. GM should be putting new transmissions in them or buying the trucks back. I'm considering contacting an attorney to inquire about the lemon law or what other avenues I can take regarding getting the truck fixed, and fixed properly.

- Warren, MI, USA

The valve body inside the transmission has failed and GM has known it to fail but they have done nothing about it. My vehicle has been in the shop for 2 months because of it and -??parts are on back order-?? it-??s terrible i-??ve bought this vehicle in august and it-??s constantly been inside the shop for various issues. My transmission lost 7th gear and it came to an immediate stop in the road because of it. tires screeching and all. truly embarrassing that you can spend 83,000$ on a truck and it be such a peice of junk.

- Flora, MS, USA

The contact owns a 2023 GMC Sierra 2500. The contact stated while driving 45 MPH, the vehicle was losing motive power. The contact depressed the accelerator pedal; however, the vehicle failed to respond. The contact stated that the engine was revving abnormally. The contact stated that the check engine and an unknown "orange-colored" warning light illuminated. The contact pulled over and turned the vehicle off and was afraid to restart the vehicle. The contact had the vehicle towed to a local dealer where it was diagnosed and determined that a valve in the transmission needed to be replaced. The vehicle was not repaired. The manufacturer was not informed of the failure. The failure mileage was approximately 25,000.

- Chester, VA, USA

The contact owns a 2023 GMC Sierra 2500. The contact stated that while driving at an undisclosed speed, the contact smelled an abnormal odor. The vehicle was taken to the dealer; however, no failure was found. The contact stated that while driving at an undisclosed speed, the contact heard an abnormal sound and smelled an abnormal odor. The vehicle was taken back to the dealer, who diagnosed the vehicle with an oil leak; however, the dealer was unable to determine the location of the leak. The manufacturer was not made aware of the failure. The failure mileage was approximately 6,000.

- Salinas, CA, USA