This old thread came up when I did a search for high altitude shift problems. I had same experience with 92 600SEL, 722.3 tranny. During my vacation trip from NY to CA I've noticed progressively worse shifting with higher altitude, above about 4000 feet. It was very rough at the Pikes Peak at over 14000 feet. I'm not sure, but maybe the problem is in the modulator adjustment? It was done at the East Coast sea level altitude and required some compensation for the higher elevations. On my previous trip to CO in ML430 (722.6 transmission) - no problem.