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.
1996 F150 Scab longbed, 5.8L, 4x4, 31x10.5 tires, 187k miles and counting. step bars, low-profile tool box, Euro-clear turn signals & headlights, Euro taillights, vent visors, class III Reese hitch, Tekonsha brake controller.
"when you have a hammer in your hand, everything looks like a nail."