Well, it looks like GM finally came through for me. After taking my car into the service department for the last 3 years with the same problem, they finally realized the cause was a bad thermostat. Now my heater blows hot air like it did when it was new, however, I still don't understand how they couldn't have found the problem the first time I took it to the dealership. I really like my car for the most part, but, for the amount of problems I've had in the past few years, my faith in GM's build quality and sevice knowledge is fading.