Here is the Lemon Laws for all the States.
http://autopedia.com/html/HotLinks_Lemon2.html
The dealership will usually try to dick you around because they don't want to have to do a buyback...........DO NOT DEAL with the salesman or sales manager. You should be contacting GM directly at this point. Get a printout of your service history from the service dept. Make sure you have every PIECE of PAPER the service dept. has given you. Tell GM you want them to but the POS back...........DON'T TAKE NO for an answer.
From what you described this truck is a DEFINITE buyback.
If you need help, send me a pm and I will help you out bro.
KS