We live at 6200 feet and regularly camp at 8,000-10,000 feet. Never had an issue with our furnace until the last trip to Rocky (8,500 ft) when the furnace would light, then flame out, try to light again and flame out. Turned out to be the gas valve. I’ve replaced the valve and things seem to work well again. Haven’t had it higher than home since then though. Sounds like you are having the same symptoms.
Atwood was nice but not helpful and I had to buy a gas valve from a third party. Here the post describing the adventure
http://www.thorforums.com/forums/f8/...irs-13240.html
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