There is a problem with the motor. That truck should get a lot better mileage than that. Ford Trucks are harder on fuel than all the others pound for pound but that is horrible. You should change the air cleaner often to keep clean air going to the motor and check to make sure the fuel system is working right. You did not say if the motor is fuel injected or not so you may have to take it to a shop and have a mechanic trouble shoot it for you because the fuel system is where the problem most likely is. Hope I have been helpful.
