[HotZ28]

A lot of possibilities here, but from your description, you either have a bad actuator, or vacuum problem feeding the programmer. Check the vacuum line from the intake manifold to the reservoir on the firewall, then follow the line inside under the dash. The programmer & actuators are located behind the glove box. This could also be a restriction in the programmer vacuum manifold. You can use a hand vacuum pump, similar to those used for bleeding brakes, to check the vacuum actuators. The one for the blend door on top of the heater core box is electric and controls the flow of hot/cold air. If the gear is broken inside, it will not move the blend door! With the glove box out, change temp settings and watch the actuators, they should move with the change in temp display settings.