Follow-up to the A/C only blowing through defroster ducts: the culprit was in fact the electronic climate control unit which is responsible for vacuum application to the appropriate servos for blending/directing of air. Pontiac dealer replaced it (I did not feel like laying upside down on my back for a prolonged period of time to try to replace - sometimes you gotta pay the the Service Dept.) However, there is a bit of good news, the part listed over $600.00 from the Service Dept., but the dealership cooperatively dropped the price to wholesale when presented with a parts quote from www.GMpartsdirect.com
for the part - saved around $200.00.
Too bad, but I doubt I'll EVER buy another GM product with either dual zone or automatic climate control. Every car I've had that ever had one of these features was problematic. Seems like another feature on which GM doesn't do their homework to make it right, are overly cheap about construction, or intentionally want return service work. A disappointment.
Thanks again to everyone who commented.