Hi Mark: Mine is also doing strange things. I checked out this company that makes new replacement air control doors for Ford and Dodge. They have videos on You Tube about how to fix the issue, which is usually broken air control doors. I looked at one of mine behind the glove box and found the door is gone...just shredded plastic on the motor shaft, and the rest in the bottom of the housing. Waiting till warm weather to fix that one! Do some checking on your truck after you watch their video. That's what I did. And BTW, Good Luck!
Website is http://www.heatertreater.net/