Never lived at high altitude, but found this on line:
http://ezinearticles.com/?High-Altitude-Baking----A-Cooks-Guide&id=50557
A decrease in atmospheric pressure will cause gases to expand easier. For your lovely meringue toppings, meringue (angel) pie shells, angel and sponge cakes, follow the following suggestions: Whip the egg whites to medium-soft peaks instead of stiff peaks. Add more stiffening with a bit more flour and a bit less sugar. Also, with your increase in oven temperature by 25 degrees F, the batter will have a better chance to set before the air bubbles
or leavening gases have the chance to become too expansive.