I'm also very happy with duramaxtuner.com. The tunes nick gave me are very smooth, powerful, egt's are down, i've gained 2-3mpg running in the light tow tune he gave me (it's the biggest one that the clutch can hold at most throttle levels) Great guys to deal with also.
Nicks tuning is top notch. Not saying others are not good. I have no reason to go to someone else. I've seen first hand his tuning last a full pulling season on a 800hp. Truck with a stock bottom end truck. He must be doing something right.