Champion 75531i 3100w Inverter Generator

I have been researching gensets for the last couple of weeks and am down to the Yamaha 2400 or the Champion 3100W. I am replacing my 3500/4000 Elim that after six years seems to have a problem with my microwave; still runs the A/C reliably, but makes the microwave count in double time. I'm thinking frequency. Anyway, the only negative I have seen on the 3100W is at higher altitudes and needing to re-jet the carb. Only saw one comment on Amazon so maybe its an isolated incident. Since I live in the SoCal desert, I can be at sea level one weekend and 9000 ft. the next; re-jetting between runs would be a pain. Anyone have any experience with the 3100w at higher altitudes?
Thanks for any advice.