The air flow seems very low from the vents. Once it started getting hot outside the ac just cant keep up. also own a 2012 Yukon Denali and the air flow is about double from this older body style vehicle. I've tried different settings and recirculating the air (seems to help a little) but the air flow is still not what it should be by any means.

Update from Aug 14, 2015: Apparently if you read the owners manual you can fix this problem. There is a cab filter behind the lower glove compartment that is pretty easy to change using only a torx driver. Once this filter is plugged air flow goes to almost nothing. Live and learn:)