A couple of things. Any starting or performance issues on this motor could lead you to think it is too tight and generating too much heat through friction? (doubtful, but had to ask) Similar to the CO test, have you put a cooling system pressure tester on the cooling system to see if you have any kind of internal leak? Any chance there is air in the cooling system? Is the temperature sensor in the same place and the same type as on your other trucks?
