Towing 6500 lb trailer. When in tow haul with cruise set at about 64 when it downshifts on a long hill and pulls and then shifts back I get a check engine light. My cheap auto zone reader shows a P038. Truck seems to be running fine and getting good milage. Any ideas or suggestions. I am in the middle of a very long trip and would like to know if something is going amiss that can be fixed.

 

Are you sure that is the right code and not P0038?