My name is [XXX] , and I am writing to formally lodge a complaint regarding a serious safety defect in my 2023 GMC Yukon with a 3.0 Duramax diesel engine. The issue involves the transmission valve body, which has caused rear wheel lockup at highway speeds. I experienced this issue at 34,000 miles on my vehicle, and it has been in the shop for over 5 weeks with no estimated time on parts availability. Despite opening a case with GM support, as detailed in the attached email transcript, I have not received a resolution. GM has refused to replace the complete transmission on the vehicle and only offered to replace the valve body. This is unacceptable as the defective valve body has already caused damage to the transmission. I also opened a BBB Auto Line case, which was closed immediately after I denied the offer from the GM support representative. This raises concerns about a potential conflict of interest, as the BBB Auto Line seemed aware of my interactions with GM support. I am seeking a complete transmission replacement with a valve body upgrade kit from NextGen transmission, which I believe would resolve the issue. However, GM has not accepted this offer. I request that the NHTSA investigate this matter promptly to ensure the safety of my vehicle and others that may be affected by this defect. If this issue is not resolved, I will have no choice but to pursue legal action. Thank you for your prompt attention to this matter. Sincerely, [XXX] [XXX] INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)