71 Corvette AC system

I used a a/c pro thermometer it said to park in a shaded area , put the AC on high , run the car at fast idle for 5 minutes with the probe in the center vent. I did that for comparison my 2022 GMC Denali truck read 40* , the Vette read 44* , the chart said it should be 45-60 so it is definitely getting cold , I think it is a combination of clear windshield, the Denali from the factory is tinted , convertible and the Denali blower is definitely putting out more volume of air.