I'd definately go with a diesel if you are wanting mileage plus power plus long life. They are more expensive, but you won't be replacing an engine at 125k. Both the powerstroke and Cummins are great pullers (ever want to throw a 32-footer behind it and go just get the proper permits. My powerstroke tows my 18-foot Olympic like there is nothing there. And for what you's get in mileage with a v-6 SUV you'll match or exceed it with a diesel. My wife had a 96 exploder for about 6 months and we dumped it. It developed more squeeks and rattles than a Jimmy Houston Bass plug. Look at www.Ford-Diesel.com for more info. I know of 4 diesel pickups with over 250k on them that are still chugging away (one has had new injectors put in it) and are abused on the logging roads daily by friends who work as timber cruisers. They might not be practical rigs howerver, for commuting into downtown Seattle due to their size if tight traffic bothers you. If you are looking for 17 mph towing rigs these are the best ones.
Good Luck

P.S. I just happen to be selling my '96 extended cab F-250 powerstroke 4x4. E-mail me if you'd like any perspective on what I think about these trucks in general. I've owned this one for over 2 years and love it. However, I'm going back to school and have to get a little tin-can 4-banger for extreme mileage. Can't afford the luxery items when not working.