In reply to Barry.

Just a follow up. Got in the Denali to go and purchase the overpriced refrigerant, turned on the AC, and damn, it got really cold just like it always has. So, it's not low on freon. Not sure what it was. It persisted through a stop and restart at least twice, and was obviously cool but not cool enough, not even close. I suspect the blending door may have been amiss, mixing in too much warm air to regulate the temperature setpoint. Or it may have been the temperature sensor was not working properly. Hard to diagnose now that it's working correctly. So I avoided the expensive stuff for today...