I have the same truck but I am not famaliar with the Texas package. It sounds like an injector stuck or a cylinder not firing. believe it or not the awesome GMC ECM can make up for a small cylinder problem for a while. There should be a code but a fouled injector would not throw a code. Alot is possible, a small piece of weld broke loose fro the tank, bad fuel, or just a bad part. I would ask the dealership to look at it outside and if they think it's serious enough and is covered by warranty, let them fix it. Hey man, you got the 10 year 100,000 mile warranty right? Good luck and God Bless.
