PhilGMCYukon

Hello everyone, I own a 2019 Yukon 5.3 4x4. (70k miles) The dreaded transmission slippage has hit my vehicle. It has become relatively undriveable. I can accelerate it to speed but slowly to allow the transmission to engage gears. I took the vehicle to an independent shop who told me they had some computer tool to manually control the transmission (never heard of such a tool), and there is an internal failure. They want $3600 to take it apart and try to fix the problem. I'd rather not let anyone start taking things apart. Took to GMC service center, and they deemed the transmission faulty and and want to replace it $6500. The warranty went out last October. I tried to petition GM for cost assistance since its barely out of warranty, and they will only help if the dealer will also provide some kind of cost assistance. Dealer said without a transmission maintenance record, I can kick rocks. Since this issue has come up, I see online now ongoing issues with this transmission with overheating. A service bulletin was released in 2021 about the trans Thermal Bypass Valve. It seems my transmission has been running super hot, and now its cooked. Anyone have any advice on how to petition the dealer or manufacture to fix this??