If you want good mileage, dont keep buying Ford. Cummins gets the best mileage and duramax is still better then powerstroke in mpg. That being said, I love the Ford trucks based on how they look, and the 7.3 is a reliable beast. Diesel is better than gas when it comes to pulling often, fuel mileage, and engine longevity.
If you pull light and buy new trucks every 2-3 years then get a gasser. I am selling mine and will stick with diesel from now on. I get 13-15 pulling weight in city and have seen 27 mpg empty on a highway run. This is with a calibrated scanguage II which is very accurate. I have several mods on my truck which make a huge difference in mpg.
Walker, Toro, Stihl