Mrs. Vicco here....In 2011 and 2013, we made trips back and forth across the Rockies, altitudes as high as 10,000 feet or more, and never had a whisper of a problem. Cruised through Yellowstone Park where some of the passes are in the 8,000-9,000 and couldn't tell any difference running at those altitudes and being near sea level at home. Problems at elevation was one of our concerns before we left and we were pleasantly surprised to learn that it wasn't a concern or problem at all.