GM-GMC: dual temp a/c, stepper motors, actuators

Question
y 2005 sierra gmc trk has dual temp and the passenger side blows hot when the a/c is on.

Answer
That is a pretty complicated system to diagnose.  There are temp sensors in the ducts and stepper motors on the mode and temp doors.  The most you can do is to check and see if you can spot any of the mode or temp actuators and ensure the connectors are intact and plugged in fully.  You may also try disconnecting the battery for a day to see if the system resets.  Most likely though you will need to visit a dealer and have them diagnose it with a scanner.
hope this helps