Haven't been there, but have done plenty of driving in the Sierra Nevada Mountains, as well as two trips to Montana, one to New Mexico, etc.  Depends on the road but I've had no problems.  Yes, you're slow, but I do encounter people with common minivans (usually some type of 6 cylinder) who aren't doing a lot better than me; I wonder if it's the gearing in the auto transmissions, the driver, the load, or a combination thereof.  I watch my tach and my temperature.  I'm down to around 45 in third gear westbound at Donner Summit on I-80, for example.  On some steep two-lane Sierra passes I'm down to 2nd gear, partly because of some of the sharp curves.  I think it's Monitor Pass and also one part of Sonora Pass I actually get in 1st gear to get around some very sharp, steep corners.  I wouldn't worry about it.  You'll get there, just maybe a bit slower than most.  

>>> Alan Gondry <agondry@MSN.COM> 08/26/02 08:23PM >>>
After spending a few days in the mountains via another minivan, I was wondering how do Vanagons make it up the mountains of Oregon?  This is for future wishful reference.  My van with a family totaling 7 had a little bit of a time.