Brake shimmy after continuous usage on long downhill grades, and excess engine rpms to climb them.
Some vans have brake heating issues and can actually warp rotors under continuous application on long
downhill grades. Would also be an opportunity to test transmission hold to assist in downhill braking.
When climbing check the tach and see how fast you're going uphill, and how high the engine is revving,
Good to know how much of a struggle it would be to climb steep uphills, and you will probably encounter
both of these situations eventually.
Also, keep in mind added cargo for traveling and full tanks (gas, propane, fresh water, gray/black) will
add extra weight, and will exacerbate any negative performance issues you might notice.
Turning radius might be good to know, in case you get into a situation where it might be problematic.
Wheelbase will usually kill your ability to turn tight corners or hairpins. Some vans are just a bit too long for some roadways, and will be prohibited like the larger class C and class A rigs, so that might be a problem if you plan to drive on any. Going to the Sun road in Glacier NP has restrictions. I'm sure others do too.
Some Sprinters have engine brakes which is a nice feature. Steve from Guelph mentioned his PW has
them and I believe Davydd's GWV does, too. Saves constantly replacing your running shoes, if you have to constantly drag one foot to help you slow down on steep downhills. (sorry, Chev chassis humor
Too bad you can't get one up onto I-80 in the Sidney, NB to Des Moines, IA stretch, or down to I-40 east of Kingman, AZ on a "breezy" day. You'd really get to feel the sway and effect of crosswinds on these beasts. Some say it's subjective, and I tend to agree. I find those 2 stretches of road nasty on certain days with a southerly crosswind (usually in the early Fall), but some folks think it's not that bad.
That's all I can think of for mountain driving. We've done a lot of it too, and it can be challenging in any vehicle, not just an RV, depending on the road, wind, traffic, visibility, weather. We came through the mountains in Colorado on I-70 in September from 90F temps in Arizona last year to snowfall at elevation just west of Denver.