So its been a little over a week now since I added the X3 tuner from 5 Star Tuning to my 09 Expedition. At first I didn't notice a significant different performance wise between the 97 Performance tune and the factory except improved mileage, but after driving it for a week I reverted to stock and YES there is a big difference. Most impressively, with the tune I am getting 19-19.3 on the highway (80mph) and 16.5-17.5 around town. This is a nice increase over stock and is a nice bonus to the additional "pep" of the truck. In my opinion, well worth $400.
anollman - do you know what your mileage was before. I have seen nothing but great things about 5 star on these forums. Thinking about trying him for my 06 expy 4x4 (11 mpgs city, 15 hwy 70-75). I know my foot has a lot to do with it, but that ain't changing - so might as well try some mods. I put the volant cai in my old f150 and response changed, but efficiency really did not. Thanks, Mike