2023 GMC Sierra 1500

I was driving down the road at 55 mph on 4/12/2026 and had let off the gas for a 45 mph zone when I experienced a violent downshift of the transmission that squealed the tires momentarily and felt like someone had hit me from behind. It startled me and caused me to lower my speed down to 20 mph. I continued driving to my destination and when I let off of the gas doing 45 mph for a slight curve I had another violent downshift that felt again like someone hit me from behind. I contacted a GMC dealer on 4/13.2026 to see if there was a recall on the transmission that I wasn't seeing online and was told no. I described what I experienced to their service department and was told to flush out the transmission fluid and replace the filter. I did experience another bad downshift at a slower speed (about 25 mph) on 4/13/2026. There wasn't any warnings or lights that came on when these three incidents occurred. When looking online I did see there was a similar recall for 2020-2022 GMC Sierra's where customers were experiencing similar violent transmission downshifts and am wondering if this issue is affecting more than just those three model years.

On March 13, 2026 I purchased a 2023 GMC Sierra AT4 Pickup with 3.0 Diesel Engine. While driving on a state highway in a 35 mph zone I started to accelerate as the speed zone changed. The truck suddenly had the rear wheel lock up for a brief time about quarter to half second then the truck proceeded on. This happened as the transmission was downshifting. Then on or about March 24, 2026 I was using the same truck and towing a 4,000 pound enclosed trailer. This trailer was hooked up within all recommended hookup requirements. In a 225 mile trip I experienced the same rear wheel lock up happen 4 random times during the trip. Once this happened at 65 miles and hour had there been snow or ice on the highway the truck may have crashed. This lock up happened while using the truck in tow haul mode. Two times it happened while the truck was being towed with cruise control active and two times it happened while not using cruise control. Truck was brought to Authorized GM Dealer and inspected and truck had no stored codes from transmission related issues. Dealer blamed this for using cruise while towing. I informed dealer this happened while not using cruise as well. Was told to turn off adaptive cruise when towing. I was unable to find anything in the GMC Manual regarding not using cruise while towing. This appears to be an issue with the valve body in the transmission and customer explained this to the dealer but they denied this claim. When these quick moment lockups happen no codes or engine lights show everything on dash appears normal. Customer is bringing truck to another GM Dealer to be tested and examined.

The contact owns a 2023 GMC Sierra 1500. The contact stated that while driving on several occasions at speeds above 30 MPH, the vehicle shuddered abnormally. There was no warning light illuminated during the failures. The vehicle was taken to a dealer, where it was diagnosed, and determined that the valve body needed to be replaced. The vehicle was repaired, but the failure recurred approximately six months later. The manufacturer was notified of the failure. The failure mileage was 81,000.

Incident Summary: On 2/2/2026, my vehicle was serviced under Safety Recall 25V-274 at an authorized GMC dealership. The service technician performed the mandated diagnostic protocol (including the PicoScope test) and informed me that the engine had "passed" inspection. No internal components were replaced; the remedy was limited to an oil change to a higher-viscosity oil (0W-40) and a new oil filler cap. The Failure: Approximately 48 hours after this "successful" recall remedy, the vehicle suffered a catastrophic engine failure while in operation. The engine failed entirely. The vehicle lost all propulsion while in motion, creating an immediate safety hazard for myself and other motorists. Diagnostic and Risk: The failure has been confirmed by a GMC dealer, who subsequently performed a full engine and radiator replacement. In the 48-hour prior to failure, there were no warning lamps or symptoms; the vehicle had just been cleared by the manufacturer's own diagnostic tools as safe and free of defects. Systemic Concern: This incident demonstrates that the current diagnostic protocol for Recall 25V-274 is insufficient to identify terminal manufacturing defects in the connecting rods and crankshaft of the L87 6.2L V8 engine. The "remedy" of higher-viscosity oil failed to prevent the exact catastrophic loss of propulsion the recall was intended to address. The replaced engine is available for inspection upon request by the NHTSA Office of Defects Investigation.

While entering the freeway at approximately 45 MPH not towing the rear wheels locked for a second, truck went into the Limp mood, and dash said reduce speed, service transmission. Dealer pulled codes, P0700 and P0747...the order says cause document #6998510."replace spacer plate, check balls and valve." Correction: DTC P0747 set Dealer told me the put the new updated valve in but I don't see that on the repair order? I asked about the GM extended warranty ( I think it's 10 years, 150,000 miles). they said it didn't apply to my vehicle?

While traveling on a major Route, the truck just turned off while driving. The truck was stuck in the middle of a two lane major route. Truck would not start or turn on. I was unable to put hazards on or put the truck in neutral. The engine siezed due to the GM recall. After having the engine replaced by a certified GM dealership, a few days later the Throttle body stopped working. Again, keeping me stuck. Certified GM dealership had to replace the throttle body.

While driving the vehicle I received dash warnings of temperature rise. Pulled over and saw a large coolant leak coming from right side of engine compartment. Towed to dealership. Dealership informed me that coolant hose coming from heater core was routed by the manufacturer so that it rubbed on the frame. Dealer indicated problem persists on all vehicles and no given, other than replacing the hose and not remedy the problem. New hose will be in contact with frame again, causing inevitable where and breakage. Dealer did not cover under warranty nor did they offer solution for repair other than replacing those hose.

The contact owns a 2023 GMC Sierra 1500. The contact stated that while driving in 1st and 2nd gear, the transmission was slipping, causing the vehicle to jerk. There was no warning light illuminated. The vehicle was taken to the dealer, who determined that the valve body needed to be replaced. The vehicle was not repaired. The manufacturer was made aware of the failure and advised the contact to file a complaint with the NHTSA Hotline. The failure mileage was approximately 97,000.

The vehicle has experienced repeated incidents of sudden reduced engine power and loss of acceleration while driving. On multiple occasions, while traveling at highway speeds, the vehicle failed to respond normally to throttle input and would not accelerate as commanded and loss of power steering making it difficult to turn the steering wheel and apply brakes. One incident resulted in throwing my truck off the road and luckily we nearly avoided a multi car collision and potential pile with my wife, 8yr old daughter and newborn son in the vehicle at high speeds up to 60/70+ mph but despite avoiding a major life threatening accident to us and other drivers, resulted in striking objects, glass and debris on the side of the road causing damage to my vehicle and then sliding to a complete stop in the ditch off the highway. This creates a hazardous driving situation, particularly when merging into traffic or attempting to maintain speed with surrounding vehicles, increasing the risk of collision. The malfunction appears related to the engine, electrical system, and powertrain. During at least one dealership visit, the reduced power condition was recreated and confirmed by service personnel. However, despite multiple warranty repair attempts, the issue continues to reoccur intermittently. Warning messages have appeared at times, including reduced engine power notifications and check engine indicators, though the condition has also occurred without advance warning. The intermittent nature of the defect makes it unpredictable and unsafe. The vehicle has been out of service for more than 30 cumulative days for warranty-related defect repairs related to this and other electrical issues. Multiple repair attempts have not permanently corrected the condition. The vehicle remains available for inspection upon request. Due to the unpredictable loss of acceleration and prior safety incidents, there are ongoing concerns regarding safe operation of the vehicle.