I don't know, my 2018 ED has struggled mightily through the "mountains" of Georgia and Alabama. I am pretty sure it would have died a terrible death in the Rockies.I've had both, a Cummins and Ecodiesel. You can't compare the two. They serve two different purposes. The ride quality on the Ecodiesel is much better. The Cummins can tear a house of its foundation, but it also consumes more fuel. As for mountain towing, we tow our travel trailer in the mountains all the time. Both are great trucks.
The 1500 is a lot easier to drive on a daily basis, but every time I hook up a trailer to it...I wish I had a Cummins.