4,000 watts times 0.775 is 3,100 watts at 7500 feet elevation.
RV Roof Top Air Conditioners Watts Required for start u____Average wattage once running
7000 btu RV air conditioner 1700 ________________________600
10,000 btu RV air conditioner 2000________________________700
13,500 btu RV air conditioner 2750_______________________ 1250
15,000 btu RV air conditioner 3500_______________________ 1500
from https://www.ramsond.com/wattage-chart/
So, if you have a 15,000 BTU AC then at 3100 watts you are 400 watts shy.
If you have 13.5 then you should have plenty if running ONLY the AC.
10 and 7 btu no problem. You obviously dont have these.
This chart assumes an average inefficient RV AC unit like dometic or coleman or similar.
I suspect a carb issue and that your motor, as a result, is not able to run at peak power.
My gen runs at about 42-50% capacity when AC is running (if at 7500 feet). Yours is needing most of its capacity to just keep the AC going.
