Altitude and appiances.

I camp at 7 - 8,000 feet frequently. The only appliance I have an issue with is the water heater. It starves for air a little bit and the flame can die. So far opening the other hatch door has always solved the problem. I think the direction of the prevailing wind is a factor too. Sometimes all works fine, so I think it is a borderline kind of thing. All other appliances are unaffected.

If you are at 6000 meters you will have more to worry about than keeping your fridge cold. Don't know if there is any place over three miles up that you can get an rv to but I could be wrong.

With the fridge, it's mostly if there is enough oxygen to keep the flame lit...at 6000ft, it's probably not an issue. Flame might run a little longer but it's unlikely to significantly impact cooling. Of course, at high altitude, temps tend to be lower so it's less of an issue.

Generator on the other hand is powered by a naturally aspirated (ie: no turbo or supercharger) internal combustion engine. Generally, they will lose 1% of power per 300ft of altitude(you can find various amounts shown on the internet but generally in this range), so at 6000ft, you will be down by about 20% on power. If you are pulling 500w on a 3000w generator, you probably won't notice. If you are pushing up against the limits, the generator may struggle.