You guys can tell yourself whatever you'd like - if you get into one of these trucks with everything working perfectly, then get into something like my 2015 F150 and compare - the HVAC in the gmt400's just doesn't move much air. It is a poor design.
The gmt400 has many strong points, but the hvac is not one of them. This is common knowledge among the people that actually use these trucks often, and also use other vehicles to know the difference.
Vent temps under 40, new ac delco fan on high. It is only ok.
I have been in the newer trucks and owned them, the AC in my Tahoe rivals both generations of Titans I have had and has strong airflow out of the vents. I have been around these since they were new, as designed they have great airflow. The van exceeds the newer trucks on a 100°F day, it has 2x as many dash vents. I have had 6 people in the van freezing with the rear unit off. I was badly sunburned and had the dash air cranked up on high fan speed and recirculate for 3 hours. Its was in the lower 60s inside the van. My aunt had a 97 Yukon from the time it was 2 years old and it would blow your hat off in airflow. The evaporator core, vent doors ans foam seals in the ventilation ducts are all places to check if they do not blow well. I use aluminum duct tape around all the ventilation duct joints on everything I go into.