07 heater problems

[stewie02]

I have a 07 4runner with heater issuses. its a single climate control system but is acting like a dual. the drivers side upper heat vents, def,and foot vents work great while the pass side is freezing as if it was set to a lower temp. that includes the upper heat vents, def, and foot vents. it also blows cold air in the back upper vents as well. had a rad and heater core flush done but no change. is there maybe a flap that is closed shut in the vent system at this point im kinda at a loss. if anyone has anything to relate to this please lmk thanks