2025 GMC SIERRA 2500 Complaints

Transmission fluid overheating, which is a known issue in other GM models with 6.6L diesel with 12 speed allison transmission. Confirmed by warning message received on dashboard and transmission fluid temperature gauge. This occurred within 3 weeks of purchase. Dealer confirmed “Valve” needs to be replaced. Part is on back order with no arrival eta. Service advisor indicates the truck is not safe to drive and remains in the service department.

The truck is not even 2 weeks old and driving down the road at less than 50mph the sunroof exploded. Nothing fell on the sunroof and no other vehicles were near the truck at the time the sunroof busted.

The contact owns a 2025 GMC Sierra 2500. The contact stated that while driving at an undisclosed speed, the vehicle failed to accelerate as intended while depressing the accelerator pedal. The check engine warning light was illuminated. In addition, the contact stated that the RPM was fluctuating while driving. The vehicle was towed to a local dealer however, the vehicle was not diagnosed or repaired due to the warranty. The manufacturer was made aware of the failure. The failure mileage was approximately 600.