A little clarification on pressure readings. When pressure is measured it is normally gauge pressure. That means that it is the difference between atmospheric and supplied pressure. The regulator supplies a set pressure above atmospheric pressure. As atmospheric pressure changes the absolute pressure changes with it but the gauge pressure doesn't.
It isn't the gas pressure that changes with altitude but the amount of Oxygen in the air that changes which causes a rich mixture. The change can cause a less efficient burner but it shouldn't be enough change to keep it from working till much higher elevation.
With this being a new camper I suspect that there is some debris in the system that is causing the problem.