The driver side and rear blowing cold air. Passenger side blowing heater hot air. Both sides set at 60 in auto. Any ideas how big an issue I am looking at

 

Its one of the four blend door actuators.... one of them is either gotten itself out of position or is failed (more likely due to the age).

Common issue really. Google GM truck blend door actuator. The fresh air/recirculate is the worst one since you pretty much have to remove the entire top of the dash to get to that one. There is one down near the gas pedal, then two others down low on the passenger side - one right near the center stack, the other I think is sort of behind the glove box.

If you hear a frequent clicking then the one that is malfunctioning has probably broken and gear. It might go away my recalibrating them though if one has just lost its positioning.

efore you spend the $$ and time on a new actuator, try this actuator recalibration procedure. I had the same problem and it worked for me. This is a common problem after you disconnect the battery.

With the ignition switch in the on position, remove the HVAC/ECAS fuse for a minimum of 10 seconds. This fuse is located in the under hood fuse/relay box.
Re-install the HVAC/ECAS fuse.
Start the vehicle. Do NOT touch any of the hvac controls. Wait 40 to 60 seconds for the HVAC control module to self-calibrate. You can also disconnect the battery for a bit to the same affect.


I forget which one does which section of the air venting but on mine I had just the opposite - hot as can be on the drivers side and cold on the passenger side. On mine it was the one on the passenger side near the center stack. They are a pain to get at regardless to replace. You need to be sure of which one it is though to be sure you get the correct replacement one. They all look similar but some of them have more wires to them than the others.

 

Thank you