I have a '06 2500HD w/6.0/tow package.....tired of the 12 mpg, not to mention gas price...a couple friends of mine have the same setup, one is an '05 and they get close to 18 mpg with factory program, I am a conservative driver and they drive their trucks like hell.............has anyone had experience with the aftermarket plug n play tuners in regards to better mpg using them on the 6.0 and if they do work, what are the better units? Thanks