You have broken actuators. I drive an '04 Yukon, and the exact same thing happened to me. The driver's side vents were blowing out hot air, and everything else was blowing cold. I put a pyrometer up to the driver's side to have it read 150F coming out of the vents.
The actuators are what regulate the mixture of warm and cool air coming into the vents. Yes, you can turn off the engine, restart, and everything will be fine. But as time goes by (took about 6 months for me), you'll literally have to restart your tahoe/yukon at every traffic light to keep cold air coming out of your vents. The problem will only get progressively worse.
When I took mine to the dealer last summer to have them look at it, they disconnected the battery, and even used their computer to reset the actuators ect. None of it works. The guy at the dealer even said 90% of the time it doesn't work.
You'll have to get them replaced. It was about a grand to do that. BUT, you can call GM, and nag them until they agree to help cover the costs. What my dad and I did was tell them that the driver side vent blowing 150F was a major safety issue, and it could put a driver/passengar in danger. It worked. We paid $500, GM paid $500. Don't let the dealer stiff you on this, get GM to help. And don't take "no" for an answer
