I owned on of the original 2V, basic crank V10s, now I have the same one you are considering.
Mileage is what people above have stated 7-8 towing, maybe 13 hiway only, moderate speed.
I looked real serious at all the possible "upgrades":
* Tuners (esp 5-Star) can help, but looking at honest (not market hype) improvements implied that the pay-off would never happen.
* Any intake mod would allow more dust/dirt in the the engine, good for rebuilders, not good for your pocketbook.
* Any exhaust "upgrade" would be because you don't like the sound or just to spend money.
Ford really nailed it with this engine.