Thanks for all the posts. It is sounding more and more like the diverter motor based on what I'm reading. The A/C works fine and blows great out of the middle vents. Heat works great from middle and floor vents. The problem seems to be the windshield vents that only seem to 'open' when in combination mode.

With the damp winters here in Atlanta I'd like to get this fixed before winter kicks in.

Anybody have any ideas how difficult this would be to find / replace?