Remember that your truck will be dumping fuel until it warms up and goes into closed loop. Depending on if it's highway or stop and go will have an effect on mileage. People who have a short drive where the truck barely or never gets into closed loop will get awful mpg. Short trips are killers for mpg, no matter what.

 

Your tires weigh almost DOUBLE what factory tires do. Now, your RIMS add yet MORE rotational weight (20% at least more over stock) to push. And the WIDER tires, add yet MORE DRAG to push.... ( Road friction) See posts here, about how Fords react to OVERSIZE TIRES vs MPG.... then pick which you want. MPG.. or a Mudder.

 

im getting around 9-10 mpg in my 1995 F150 5.0 auto 4x4 extended cab long box 3.55 towing a 5000lbs trailer havnt done a test in town lately but have got as high as 19 on the highway

 

Wow, I have 94 4X4 with a 302 and the best I ever get is 15mpg. The suburban with 350 gets 18 mpg, way heavier than the F150.

Side note on getting better gas mileage, install a vacuum gauge, monitor your driving to get the highest vacuum and you will get the best gas mileage.

 

If one cares so much about MPG, a truck is NOT the vehicle for them. If you manage double digits city in a 20+ year old truck driving in the city, be happy.