It's all electrical so it's relatively easy to diagnose.
Try removing the hvac fuse from the passenger side of the dash for about 2 minutes, then put it back in and start the car, Leave it run for at least 2 minutes and do not touch any controls while your waiting. This will recalibrate the position of all the flap motors and climate control.
If it is still doing the same thing i would guess the temperature control motor is bad and you can get one from almost any gm car made since 2004 to replace it and repeat the above calibration procedure.
Let us know how it goes
