I purchased a tuner from diesel domination for around $400. Just Google diesel domination for more info. My duramax has never had so much power! You plug it in under the dash and follow the instruction manual,you can tune for several applications. One thing I did learn was you don't want to take out your ECM and send it off because if you ever have to take your truck back to the dealer and they flash your ECM and find you've modified it,then all warranties are void. With your own tuner you store all your stock info so if you ever need to you can download the stock info back in.

My truck is a gas pot. I ended up buying a Banks power pack system and that included a CAI, shorty headers, monster muffler, huge tailpipe, and a programmer. I also installed aluminum wheels to lighten the rotating mass, installed a fiberglass topper instead of the steel work one that was on it when I got the truck. All of this did a Lot for it and made a big difference. So much so that my buddy made me an offer that I couldn't refuse and he bought the truck from me. Now I have to tune a 2008 Dodge Ram with the 5.7 hemi to get more jam from it. Probably gonna get a programmer and a CAI for it as well at a minimum. Sounds like your truck is good now and I was aware of the programming ECM and losing warranty coverage or the program itself if off warranty and it is in for other work and they update ECM due to other reasons for driveability or emissions reasons because of a service bulletin or recall that one may not be aware of when taking the truck in for something completely unrelated. Thanks for your input.