Look into leaning it out more. Dunno what model yo have, but some (all?) have an altitude adjustment screw.
However, it would have to be running VERY poorly, very rich to not have enough snort to at least run the microwave, even if it's a little 2500W unit.
Check spark plug. If it's fouled and or dark/black then it's running rich. Insulator ideally should be a cardboard brown color. White = lean, black = rich.
Air cleaner presumably is clean since you just had it serviced, but running no air cleaner could help diagnose, it might get a "little" more air, not significant though.
Fuel, if it's fresh shouldn't matter. Octane requirement goes down as altitude goes up. Guessing it's gasoline though since you didn't specify, but you said it's in a moho.
Possible carb plugged?
And if it's LP? I'm not familiar, but presume they have an alt adj as well?
