On the first issue, you could have two possibilities. The thermostat may not be regulating temp correctly, and the air is warmer on the passenger side because of its proximity to the core, by the time it reaches the drivers side it is cooled even more. Or there could be a fault with the dual zone system, where one blend actuator is faulty and not working, or overtraveled and defaulted to full cold. The latter will set codes, they could only be checked with a scan tool.
On the second issue, does the blower noticeably slow down as well? I did a bulletin search, and found this. It regards whether or not there is a cbin filter installed.
#PI01797: Missing Pollen or Cabin Filter - accessory air heating HVAC condition automatic bilevel blower cool cowl defrost dirt door duct evaporator external fan heat heater manual no odor passenger - (Feb 26, 2004)
Subject: Missing Pollen or Cabin Filter
When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
Missing pollen or cabin filter
For 2003 and newer models of the Buick Rendezvous and Pontiac Aztek, the HVAC case does not contain a pollen or cabin filter although the case has the provision and the door is marked "Filter". With the filter removed, air flow into the vehicle is improved when using vent mode and high temp settings. SI and the owners manual do not refer to this deletion or give instructions for installing this filter. Installing this filter may reduce airflow from the IP center vents especially on warmer temperature settings and cause customer dissatisfaction.
(2003-2004 Buick Rendezvous) and (2003-2004 Pontiac Aztek)
Friday, January 29th, 2010 AT 8:21 AM