Chucko; If I'm not mistaken, vehicles over a certain Gross Vehicle Weight rating are not required by Fed law to display fuel mileage. I can't recall the GVW, but I do know that a F-250 is one that doesn't require it. I had a 5.4 in my '99 250. With a Haulmark 7X14 trailer in tow I was down to 6 mpg and really didn't want to drive over 65 with it. I had a trac-loc rear end that even required 4.10 gears, that is the only gears I could that year. After a trip to Denver and back, that truck was history. I now have a 7.3 Stroker that I'd never trade for a gasser. The best I ever got with the 5.4 was 14mpg. Thats the worse I get with what I now have pulling my tractor/trailer where ever I want at 70 mph. And I mean 70 mph. I might not be smart, but I'm not a fool either. If you are just lightly loading your vehicle, the 5.4 will probably work. If you move heavy loads, forget it. The megabucks extra for a Stroker may or may not pay for itself, I don't look at it like that. If dragging alot of weight, the only choice is the stroker. Consider what you'll be using the truck for, and decide as YOU see fit.
Now to get back to the original question, you probably expect around 14-16 mpg with the 5.4. Good luck with whatever route you go. My statements about the 5.4 I had are true to MY experience. Maybe someone else has had a happier experience. Diesel versus gas is a lot like arguing Ford versus Chevy versus Dodge, it all comes down if your happy.