heater still stuck 2000 silverado

Just as every other silverado(2000) mine to wont go from heat to air for 3 days. The air flow control from defrost to frontal cabin wont change also for a good while. The dash controls are new and the damper control under the dash on pass side is also new. Still same problem, Ive owned 7 new chevys from 92 up and this 2000 model must have been built by MOPAR cause Ive had nothing but trouble,time for a TITAN I guess. Any ideas on anything else that could be wrong???

There is a top damper/control gate as well. Not sure but could that contribute to the lack of control b/w defrost and cab and/or floor?

I had similar problem where the bottom was bad, replaced it and all has been well. Remember, all these are man made so something is bound to go bad at some time. Best wishes!!!