I have a 97 crew 4x4 F250 and get 14 MPG in the city (35MPH) and 18 MPG on the HWY(70MPH) . That is at sea level with a pint of 2 cycle in the tank and a little DieselKleen.

Up in the mountains 3000-8000 feet on hilly roads going 40 MPH consumption goes to 10-12 MPG.