I have this happen to me a couple of times and I cant figure it out. Ive been towing a trailer about (7-7k pounds) and the wrench light will come on and I will be stuck in 3rd gear. ive had it serviced regularly and it only has 38k on it, its a 12 crew cab with the 6.2. I even had the dealership service the transmission, and it still happened. not sure what to do, any advice will help.