Transmission shifted harder at altitude?
 

I recently drove back to Colorado from California. The transmission in my 300E was shifting VERY firm at altitude, not banging into gear, but it was "kicking" a lot harder than normal especially at redline. Very worrysome, especially since It turned 200K on the way out, was just waiting for *something* to go wrong. The car lived at altitude for 20 out of it's 21 years, so it should be used to it.

Anyways, I'm back at sea level...and it shifts like butter again. Weird. :confused:

Given that transmission modulation pressure on your model is controlled by engine vacuum, this is a not unexpected result:
Effects of Atmospheric Pressure on Vacuum Level

Interesting. I kinda figured it had something to do with vacuum/altitude. Does the modulator self-adjust itself after awhile, or? It never shifted like that at altitude before in the five years I've owned it...

Its a set value. Over time the engine will lose vacuum, so it may need a SMALL adjustment to compensate for the lack of engine vacuum you have today compared to a long time ago.

Well thank god I don't live at elevation anymore. 20% power reduction is no joke. The first pass I tried to make on a two lane road in Colorado scared the sh!iat outta me! :D