I had one done on Saturday. Previously I had attempted to mess around with a buddy's EFI Live, but it really wasn't very effective. My tuck is a 06 with the 5.3, 3.42 gear's, and 255/75r17 tires.
I went down to Novi, talked with Jeremy a while, who's a nice guy, and really knowledgeable about tuning. It seems he usually tunes for a more street oriented crowd, but we were able to come up with a strategy I'm happy with.
Before I went in, my speedometer was off by 10%, he got that corrected, I had an EVAP solenoid code, that made the pump shut off non-stop while fueling, he killed that, pumps gas fine now, traction control is killed, Displacement on Demand is killed, I'm not blowing big clouds of smoke coming out of cruise now.
All in all, for 100 bucks, I'm really happy. I didn't gain 567 RWHP, or probably any, but it drives much nicer now. Holds lockup where before it wanted to kick down two gear's to keep 60 mph on a two lane highway up a slight incline. It has improved my MPG by about 1.5. My speedo is accurate. The thing is really a pleasure to drive now, whereas before it was quirky to say the least.