OK Here's the skinny: Flatlander from St. Louis decides to visit old haunts in Denver by driving I70 to Salt Lake City then North to Idaho Falls, ID (visit brother) then drive to Ft. Collins Co to visit friends and tour Rocky Mountain National Park (drive the highest highway) then return to St. Louis. Absolutely No Problems until I start to pull the first mountain outside of Denver...Car loses power - misses a lot, then dies. AAA to the rescue - directs me to a shop in Golden, Co. process of elimination diagnosis - failed mass air regulator. Repair made, pull out of Golden-head west again, "Service Car Soon Light Appears" return to shop which then runs a smoke test and determines that the "dip stick tube" o-ring is leaking (only, no other leaks). Replace the o-ring, run 4 cycles without the tripping the Service Car Soon Light". Cool - head west - pull Vail Pass - no problems, pickup my wife in Salt Lake City off to Idaho - no problems (tire problem aside) what-so-ever for six days of driving. Then on the return trip, I get the bright idea to visit Estes Park/Rocky Mountain National Park. Approximately 11,300 feet - The "Service Car Soon" Light trips again. I drove back to Ft. Collins without a problem - (no engine misfires), and intend to return to St. Louis in a couple of days. Has anyone experienced this type of fault with mountain driving? Any suggestions?