I also picked one of these up... granted I would never pay 350+ for one.. your performance shop is raking you over the coals as I paid 180 for mine in Alberta.
It definately doesn't give the truck any more power.
With the stock truck and 22" wheels I could barely get the tires spinning even using the brake. Install the sprint booster and simply flooring it from a stop will send the rpms climbing and i'll leave a good 10 feet of rubber. Add a little brake into the equation and it's even better.
There is zero throttle delay anymore. When you want to go, it goes. But like it's been mentioned in the posts above, the pedal is extremely sensitive at the extreme setting.
The only problem I have with any of these trucks is that there is no way to prevent an upshift. In my 06 srt8, the diablo tuner allowed you to hold a gear until you shifted up. The reason it's annoying is that when you take off from the box, the tires spin and it shifts to 2nd... tires stop spinning and the computer says "hey we're still going slow enough for 1st gear", so it down shifts again for all of a second or 2, then shifts back to 2nd.. I wish there was some sort of trans tuning you could do with the trucks, as there is with the LX platforms..