If your AC air flow has dropped significantly, it is likely a broken recirculation door that has now positioned itself over the fan. It is an easy fix to remove the broken door thru the fan housing. Simply remove the (3) 8mm hex head screws holding the fan in under the glove box. Reach into the duct work and pull out the broken door. It will be totally loose as it breaks off at the hinge. It may even fall out when you drop the fan. The AC/heat thru all sections (defrost, feet, straight ahead) will now work normally on the selector. The broken door is used only to stop outside air mix in order to aid in faster heat or AC when outside air is extremely hot or cold. We have had three trucks in my arena of friends with this problem. I would not replace the door, as the same problem will happen again when the new one breaks. Later model trucks (possibly after '08) have a different system. We have had this problem with our '06 and '07 models for sure.

 

Outstanding hint. Fixed my truck in about 5 minutes.
Thanks