So, I just installed built trans I bought from another member. It has all of the goodies including a GMR 1" chain. It was torn apart and verified by a local shop and reassembled with new gaskets. WE got it in and it drank down about 10qts of fluid (torque converter still had fluid from the stock trans. We had it on the lift and I shifted through all of the gears to let the fluid go throughout the trans. We get it on the ground, and I start driving home. After about 20 miles of easy cruising (50-70 mph and no real hard driving), I leave from a red light, get to about 40mph and then lose all gears. I pull over in a parking lot and pop the hood. I pull the dipstick and it's burning hot and there is steam coming out of the tube. There is still a little fluid on the end of dipstick, so it wasn't bone dry. I parked it for the night and came back in the morning to have it towed to a friend's shop.
What could have caused this? Clutches? Torque Converter?