HVAC system Mode Door.
 

Anyone ever change theirs out before?

My heater is only working out of the middle vents and not out of the defrost or floor so I am pretty sure the door is shot.:argh:

i had the same problem with my 93 ended up changing the whole control center got mine at the junkyard for 10 bucks changed it in a couple of hours

Got a friend with the same truck?? Swap out the dash controller and see what that does. The door motors are pretty bullet proof. I've seen pens dropped into the defrost vent and get lodged in the door also.