I used to live in La Paz. I had HAPE (high altitude pulmonary edema) or pneumonia (similar symptoms) twice and the second time almost killed me. Fortunately I was at home (just got back from the States), so it was a quick trip to the clinic where I spent a week hooked up to O2 and and an IV.

My point is unless you are sure you can handle the altitude, traveling in the Andes is not a great idea. I was as high as 16-18K or so a number of times, but that was after being there a while-not weeks, months.