I am not a mechanic, but I have always done most of my own repair work, mostly due to cost. Just throwing this out as a possible cause. Could it be that the thin mountain air is causing the lean codes? If it is, then I don't know that you will be able to solve the issue, other than to not "pull" up the mountain.
Another suggestion, you could send a pm to NGM, he is a mechanic and a moderator here. Ask him to have a look at your post and give his opinion.