Your paying for the exact same computer in the truck already...save your money and find a competent tuner locally. You should find custom tune in the $300 range w/ free updates as your needs chage.
I know this guy does alot of mail order tuning and sponsors a number of forums.
http://gowheatley.com/home.html
Check out
http://www.performancetrucks.net they have a pretty damn big tuning and diag area.