These Spartan tuned 6.4's are seriously good trucks.
Oh I'm on my mighty Chevy high horse that 'oh no ford can make that with just a tune/exhaust' well let me find you some links...
http://www.thedieselgarage.com/forums/attachment.php?attachmentid=383&d=1230429111
Which is from this link
http://www.thedieselgarage.com/forums/showthread.php?t=267&page=7
(if you look at those timeslips that guy Pahrump is running low 13's with stock gears and 38" tall tires (275 tune/intake/exhaust)
Sorry I can't find more but I don't have time. If you search around the diesel garage there are dozens of people running this spartan stuff getting 18-20 mpg and putting out over 500 RWHP with just tune/exhaust/intake. It's not heresay. I'm sorry all of you guys think yourselves to be experts on things you have very little or no experience with. Do some research next time before you start spurting out incorrect facts.
There are dozens of these graphs floating around from all sorts of different people but like I said I don't have time to find them all.