I've been out to the Rocky mountains several times, Mostly through Colorado, but I've been through the northern Rockies too. I have been to northern California, but I wasn't driving that trip.
I always engine brake all the way down the passes, only touching the brakes when I absolutely have to. I've never had them over heat, never had them fade. Obviously having a manual makes things much easier, but I've done this successfully in an auto.
I'm not saying it isn't possible to make your brakes fade with a DD car, I'm saying that in everyday driving, there should be ample time to cool the brakes down to avoid them overheating.