I'll just pile on a bit here. We have driven over the Rockies, through the Canadian Rockies and down into Presidio TX in both a gasser (8.1L GM with Allison) and in our current DP with Engine Brake. No problem in either coach towing our car behind (RAV 4 behind the gasser and Jeep Wrangler behind the DP. The secret is to drive down the grade at the speed you came up, in the gear you came up. So if I crest at 30 mph in 2nd, that is how I start down and I use engine braking or EBrake to hold the speed. If the speed rises I apply the brakes firmly just long enough to get to 5 mph below my desired speed. Never let it get away from you, it will be a wild ride no matter what system you have, not that I have any experience of that.
