I didn't dig a lot into this as I ended up paying a mechanic to fix it. But the symptoms I suffered were running AC because it gets freaking HOT in Texas, and having the driver's side -- and ONLY the driver's side -- blow heat; everyone else got AC. But, from the information I have read across multiple GMT800 groups, there are three doors/actuators/whjat-have-you in the front on the GMT800 trucks; one at the driver's footwell, one at the passengers foot well, and one completely behind the dash. The one behind the dash is rated at 9 hours of labor to disassemble the dash, replace the problem part, and reassemble the dash. As an aside, and this is a wild-ass guess, there are separate units conditioning the air between the front and the rear systems. There is a part, for example, in the right rear wheel well (inside the cab) that has something to do with air going to the back part of these trucks. So I am thinking that bmishoe's problem is something under the hood as opposed to a door issue. But, at this point, taking it to a mechanic and getting it professionally checked would seem the wisest course of action. The trick there being making sure you had a mechanic you can trust. I don't know where he is located, but if he is in the Dallas/Ft. Worth Area of Texas, I can direct him to an honest mechanic.