Help!! New to the forum. I have an 88 F350 dually 7.3 no turbo, c6 3.55 gears. Only getting about 9 mpg unloaded. Newly built engine new injectors, older IP but in good shape, timed perfect with ferret meter, turned down. Fires right hip cold or hot with out throttle. Only a little black smoke when i get in it. Otherwise burns clean. Mostly highway. 60 mph about 3000 rpm, 650-700 deg. On the pyro. I know these trucks aren't known for fuel mileage. But really? 9 mpg unloaded. I'm only gonna get like 6 mpg hauling my travel trailer. Any help would be greatly appreciated.