The transmissions on '08 and later 6.4L equipped trucks, seem to handle power upgrades pretty well, from what I've read. Spartan diesel has one of their 6.4L trucks making way more power than I am, and they've had no breakages so far. At least that's what they claim. Also, Diesel Power magazine did a build up of these trucks, and were claiming between 600 and 700 horsepower. I will say that even though I haven't broken anything as of yet, The truck shifts pretty hard when set on the highest level. It takes a little getting used to. According to Spartan, the 310hp tune was not designed to be used for everyday driving, but for racing only. However, I like to have all that power on tap just in case an errant dodge or chevy wants a challenge. Spartan also offers an upgraded TCM for these trucks, and when coupled with the tuner, it's supposed to be good for an additional 2-3 tenths reduction in quarter mile times. Plus it smooths out the shifts, so they're not as harsh. Price last time I checked was about $600. It wasn't worth it to me at the time, but I may add it in the future.