I live at 4,000 feet and went for a run at 7,200 feet recently, and it was a very different feel. I just could not catch my breath.
I went for a run at 8400 feet in Tahoe and just could not watch my breath....
Same here when I was stationed at Kirtland AFB NM..... Albuquerque . I lived behind the Manzanos at Zuzax NM ..... our daily PT down at the base was 3 miles out and 3 miles back..... it was easy at 6300 ft altitude to paratrooper shuffle 6 miles each day.
But lord help me.... we ran this race each year that almost killed me every time I tried and trained for it....
http://www.abqroadrunners.com/la-luz-trail-run.html
http://www.abqroadrunners.com/elevation-map.html