Must I alter cooking times at higher elevations?

Yes. As you have probably experienced, it takes much longer to cook foods such as beans and brown rice at higher elevations. This is due to the fact that the temperature at which they come to a boil, and therefore cook, is lower than it would be at sea level. This makes a pressure cooker extremely valuable at higher elevations because it allows the cook to raise the cooking temperature and this speeds cooking. In order to compensate at elevations above 2000 feet, the cooking times in a pressure cooker must be altered according to this formula: for every 1000 ft above 2000 ft elevation, increase cooking time by 5%.