We live at 1052 feet elevation in Oklahoma City and spend several weeks in the summer in the Colorado and New Mexico mountains. One of our favorite campgrounds is at 10,500 feet and we have never had any problems with the refrigerator in any of our RVs. We are always boondocking and therefore using propane.
I have never been a fanatic about being absolutely level but I have found that the refrigerator needs more attention to leveling at altitude than at lower elevations in my experience.
Our gensets have an altitude adjustment on their carbs but not so our refrigerators. You gotta keep that flame clean and shooting pretty straight up the tube for maximum efficiency. Any inefficiency is compensated for in part by the fact that it is cooler at altitude and so the refrigerator doesn't struggle as much to keep cool as when the ambient temperature is high.
As a flat lander in an alien environment we always take it a little slower, drink a lot of liquids (particularly plain old water) and make sure our sodium and potassium intake is above normal. When I was a kid working in the hot Oklahoma sun in the oil fields while going to school we always took salt tablets to retain fluids. So did athletes. Now, everyone is "salt sensitive" and you don't hear of them much, but they sure kept up your hydration.
Paul