Mountain Driving in Colorado Rockies
I was going to refer you to some other posts on Colorado mountain driving, but I think they were lost when this site got hacked a few weeks ago.
My wife and I have driven extensively in the Colorado Rockies, including Trail Ridge Road, Pikes Peak and around Breckenridge, Frazier and Granby. Our 2002 Prius handled Pikes Peak (14,110 feet?) and Trail Ridge Road (a little lower) fine. The only minor inconvenience was approaching the Eisenhower Tunnel from the west on I70, coming out of Dillon.
That is a long steep grade, and the batteries ran out about 2/3 of the way up. However, we were able to hold the speed limit on ICE only, passing semi's and RV's with caution (since there was not much reserve passing power). And, the batteries recharged within a couple of miles on the downhill side going into Denver.
I consider this one minor inconvenience for only a mile or two in 48,000 miles of driving the Prius. We have been over the Grape Vine north of LA on I-5, most of the mountains in Arizona, many of the National Parks in southern Utah (including Bryce, Zion, Arches and Monument Valley -- all relatively flat), and over many of the mountain passes in New Mexico; all without any difficulties.
In fact, on all grades except the western approach to the Eisenhower Tunnel, we were able to pass at will. And, even on this stretch, our Prius overtook many "ordinary" vehicles having difficulty with the altitude and grade.
I don't think you have to worry about driving a Prius in the mountains...