We just did that run over the Rockies a few weeks ago from Arches National Park into Colorado Springs on I-70. The hill just before the Eisenhower Tunnel was not fun... we did 37-39 mph going up that hill and was watching the tranny and engine temps climb but they eventually held before reaching the tunnel and getting too hot.
The next day we got the quarter size hurricane hail in Cripple Creek, but we were already unhitched and were able to get under a gas station canopy just in time. The fiver at the campground only had damage to one of the bathroom vents, could've been a lot worse. We had a great time, but wouldn't want to do that hill again towing the fiver :-)
Oh I almost forgot; on the downhill side of the Rockies on I-70... the slow lane is so heavily grooved by the semi's in some spots, it wasn't the downhill speed that was an issue (the Allison did its job nicely), it was trying to keep the rig going in a straight line due to some of the grooves. Where the road was smoother it was great, but they really need to fix those grooves in that slow lane, it is really bad and dangerous.