Re tune your ECM after you get a high flow intake and exhaust system to take full advantage of the two. Here is a link to Pcmforless, there one of the better ones out in the industry in to re turning ECM's for 1996 + OBD II system cars and trucks out there.
Good luck and it is one of the best investment's you can do and is better then the Generic OBD II power programmers. The ofter market power programmers still have parameters that you can not over ride to achieve a custom tune to your preference of performance. I my self have a HP tuner that can custom tune my ECM to any performance is like to have with my Jimmy, regardless of emission standards.
As to the warranty aspect of your question I would have to assume that it would clash with your warranty. You may want to speak with someone in the service department about this.
So just to be clear no one knows if for sure it would affect the warranty? Even if the mechanic was certified by gmc and stayed within the parrameters of gmc. Is it best for me to call and if so what number and/or should I visit a dealers service department?