It's likely the problem is the rear blend actuator or could be the control.
Here's the cheapest thing to try first:
The actuators are notorious for losing calibration so hope this takes care of it, otherwise you may need to replace the control.
Take the negative battery cable loose.
Remove the actuator. I think you have to pull the interior cover off in the right rear to get to it.
Mark the position of the drive gear on the case and the drive gear shaft with a sharpie.
Remove the screws holding the actuator together.
Remove the cover.
Mark the position of the sensor wheel that is driven by the larger drive gear by making a dot on the gear and one on the circuit board.
Pull the little gears out. They have different diamter shafts so only go back in one way. Leave the grease on them.
Pull the larger gear out.
Spray the remaining sensor with a little WD40 and rotate it back and forth to clean the contacts that are on the bottom side of the gear.
Reassemble making sure the drive gear and sensor wheel are in the original positions.
Reinstall the actuator.
Reconnect the battery cable and turn on the key.
Do not adjust the controls for about 1 minute.