You're not going to get a 50% (7mpg or so) improvement in fuel mileage from bolt-ons and a tune. Sorry to burst your bubble. If that were the case Ford would have done that to begin with.

At best I see 2mpg maybe 3mpg if you spend a thousand bucks or so. That's a 15% improvement in mileage and is more of a reasonable request.

People with trucks always make me chuckle. For some reason they all think slinging around that amount of steel doesn't come at a cost

You could always go coocoo for coco-puffs and try one of those water4gas setups, played with one years ago, kinda worked, but was a melting pot inside your engine bay and too much fiddling.