i have used many many of matt's tunes...
his tunes are some of the most powerful tunes available for the 6liter nothing i can say bad about them in the power department, but in the year that i ran spartan tuning i ended up going thru 4 trannies... 3 of them fully built.
i am now using eric's tunes, from Innovative Diesel, and the tranny tuning is much more in sync with my truck and my driving style. i'm not saying matt's tunes suck, as i know many people who are still on their stock trannies and using his tunes, but just my personal experience is that i am much happier with erics tunes... and with my current NONVVT setup, i actually have much more usable horsepower with Innovative tuning.