I have driven up Pikes Peak twice with a truck. The elevation is 14,110 feet high to the summit. The first time, years ago, I drove up the mountain with a carburated truck, not fuel injected. I barley made it to the top because the air thinned out so much. The next time I had a fuel injected four wheel drive truck. I put it low range after 10,000 feet and had no problem.

I bet that would be great on the ATV.