Heater question

During the winter when I turn the heater control all the way into the red (completely to the right) and have the blower on 1 or 2 get warm then want to turn it half way and turn the blower off. The truck still blows heat like it is all the way up. It even blows hot if I turn the control to cool and have the AC on. Any Ideas?

Did you ever find the cause to this problem? My 00 z71 has the same exact behavior as described here.