There are many options out there. Do you want canned tunes or custom? How much do you want to spend? Programmers like SuperChips or Hypertech can run in the $300 - $400 range - Custom tunes probably higher depending on what you want. There are some vendors here that can give a better idea. They can be found by clicking on the "Forums" link in the top nav bar and scrolling down to the Powerstroke.org Supporting Vendor section.
Then, there's the "DAAAAAAYYYYYUUUUUMMMM" Factor. That's the thing that hits when you realize you have more power. The result, though, is in indirect proportion to what you want to achieve. You want BETTER mileage and you're getting worse. Until the Dayum factor wears off (for some it never does) you won't be seeing any improvement.
Good luck in your search...