Here's a post from a57chevy43 on the original PRC site - only thing I found with the search feature.
"A polaris guy told me that the polaris fuel injection computer learns every time it is turned on. Meaning that it learned the altitude, fuel/air mixture, air temp, etc every time you start the machine. Maybe it needs a few seconds to learn and smooth outh out for optimal performance. EFI's like in yamahas and can ams and others cant learn or adjust. They are set at certain peramiters (misspelled I know) and the computers have to be reflashed at higher elevations to run properly. My RZR has always run a little erratic at start up but would then smooth out after 5 or 6 seconds and be good the rest of the day. If I went out and rode for a while and killed it then restarted it right back up, no problems. But if I put it up over night and got up the next morning to ride it would be erratic again. As I found out the air temp was different and the computer would relearn for optimal performnce. As long as your RZR runs good after a few seconds I wouldnt worry too much."
In a separate post Martymoe agreed that altitude should not impact the Rzr. One other poster indicated that you will lose only 1% of horsepower for each 1000 feet of elevation, and that horsepower change may marginally impact clutching (although they weren't completely certain of the mechanical rationale).
Have fun, and climb and descend safely.
