If you are baking any recipe, including this yeasted gluten free bread recipe, at high altitude and the recipe, like this one, wasn't developed to be made at altitude, you must make certain adjustments to the ingredients and/or method to achieve the intended results. Altitude is one condition that I simply can't recreate, though, so I'm not able to test any of the possible modifications. However, other readers have told me over the years that their "regular" altitude adjustments work just as well in my gluten free recipes as they do in their conventional recipes. This King Arthur Flour guide for high altitude baking seems comprehensive.