Hello, I have a 2000 Silverado with a heater problem. When I leave the heat completely off and drive for a while (while at operating temp) and I turn the heat on it's nice and warm for about 10-15 seconds and then goes cool, not super cold but certainly not hot. If I repeat it it does the same thing. I had the heater core flushed some time back and I changed the T-stat. After that the heat worked great. When I feel the heater hoses both seem to be at the same temp. I have not overheated it ever since I have owned it (which is a long time now) I can watch the temp gauge and it seems to come right up to temp no problem. Could the t-stat be bad? where else could the problem be? I am not losing coolant at all, and my blend door seems to move fine (hot/cold).