Start with the simplest first. Check the coolant level (at the radiator, don't depend on the overflow reservoir). Happened to my '06, reservoir showed full/cold, and it took over 1 1/2 gallons of antifreeze in the radiator. Same problem, no heat - not saying this is the problem with your truck but worth checking. Only problem I had was getting the proper coolant, and I had ended up getting it from the Ford dealer, no place sold it near me