I live in Laramie, WY at 7200 and a friend comes from Columbus, OH (600-700) to hunt every year and we hit some good mountains. Even though I live here, I still run a lot. In fact both started training for this year on December 1. Sounds corny but we email each other about our work our to keep us honest. I think HIT (high intensity training) is the most important. I can run about 4 miles at a decent pace but I learned quickly the slow steady inclines will hurt you quick so you really got to press yourself to be ready. Here is a sample work out that I do at 7200 feet. run on a treadmill at 8.7 for 1 min 0 incline then with a 10 sec break (to set speed) I go 4.5 speed walk at 8 incline for a min then rest a min.... repeat till failure. I find this really helps my lungs. other days I will lift weights and do a 60 min walk at 5 incline. I have heard of people back east have gone as far as using a surgical or dust mask to limit oxygen when running/hiking but I think that is dangerous. I would just work sprints or going fast on a stepper into your work out and push yourself for quick recovery (interval training) and do plenty of squats or lunges and work in walking with a large incline.