I would say it was time for a reconditioned controller, but it could be most anything, and without watching the inputs to the controller logics and seeing what changes, I would not ever be sure what it was.
My question [reason for posting] is;
How did you find that hitting it with a hair dryer would fix it?
Do you normally have a hair dryer handy for troubleshooting??
does this truck have a curtis controller? ?checked the pin connections on the molex connector?