2003 Tahoe climate control

I have a 03 Tahoe LT 5.3 V8 with 48k and am having trouble with the Tri-zone digital climate control. The AC does not work in the rear zone, it only pumps out hot air, or the outside temp air. It never gets cold. The front zones AC is not very cold, though colder than the outside air, and the fan strength is very weak most of the time and when it does work its full blast. We have tried to work the system manually and using the AUTO mode with no luck in the rear zone and little luck in the front zones. Any help would be greatly appreciated.