I haven't got a dually... and I don't really have enough miles (20K) on mine to be any kind of longevity test.. but the majority of them have been towing, from home in the Black Hills, to the Grand Canyon and Moab, to Yellowstone and the Grand Tetons, and to Glacier National Park. So mountains are familiar territory.
I've been extremely pleased with my Ram. It's been a pleasure to tow with, and makes a pretty fair daily driver as well.
To be objective for a moment, I'd probably have the same experience if I had chosen one of the other brands. All three are pretty impressive trucks these days.
Drive 'em all. Buy the one that fits your budget the best, or puts the biggest smile on your face. Chances are, one of them will feel "right" to you. It's a little like buying shoes... you can get so wrapped up in the details that you forget that being comfortable is the most important thing.
