The best cold air intake i know of is the stock air box you have. Open up the air box and remove it from the engine bay, there is only one bolt holding it in.
Notice the front of the air box having a restriction tube, the best mod you can do is to cut the front of the air box open where the tube is. Make sure you don't cut the top of the box where the air filter seals to, with the tube out. It's wide open to take cold air on from the air vents behind the head light and keeps the heat out from the engine and radiator.
It's free to do and take about 30 min to do, you can use the paper filter or a stock K&N air filter if you like. You will not notice any difference in performance unless you tune your PCM.
http://www.pcmforless.com/ You will notice a different sound from your engine and exhaust, when you cut the front of your air box out below the mount it get's really loud about 1750-2000rpm and up of air getting sucked in. Send a PM to
http://gmcowners.com/gmc-forum/private.php?do=newpm&u=9224. He did his with a stock exhaust system and he's happy with it.
Good luck and hope this helps.