My 08' GMC has been backfiring and hesitating pretty bad the past few days... I have no idea whats going on with it. I have tried HEAT fuel treater in the tank thinking I had water in there... no change. Its been down to 18* or so recently, when the cold weather hit is when the truck started running poor. Today the sucker backfired and blew my CAI off. All I have is a tune and CAI, no major mods.