2004 GMC Sierra 1500 Ext Cab, 5.3 , 44500 miles, whiel driving down road, with ac on, driver side starts blowing out heat while passenger side still blows out cool air what is cause?

while driving down road, driver side air blows out hot air, passenger side
continues blowing cool air, I have to shut truck off and restart and cool air blows
again. other issues are also occurring. driver seat will not go back, the switch
on side, to go back, you have to push it forward, to go forward you have to push
it back.