Providing the year, make, and specific model of your truck will help people advise you better.
It sounds like you have dual-zone climate control that's standard on Eddie Bauer, XLT Premium, Limited, King Ranch, Platinum, and some newer XLT trucks with the 202a package. If so, then you have not one but TWO blend door actuators that can fail. The one for the passenger side temperature control is on top of the HVAC plenum and so it's easy to access and replace. Unfortunately, the one for the driver's side control is on the bottom of the plenum crammed up against other parts such that the bolts are inaccessible. As a result, it's a nightmare to access without pulling the dash out.