The rule of thumb is to go down the hill at least one gear lower
than you went up the hill, towing a trailer is not a race to see
how fast you can get down the hill, it is how safely you can get
down the hill .....
I always start off the top of the hill slowly and as I progress I
tap the brake's every so often as soon traveling down the hill
but not laying or pressing down to hard on the brakes for a
long periods of time. This way you do not heat up your brakes
and it also keep your RPM's down.
WARNING if you keep braking on a say 6 or 7 percent grade by
the time you get two thirds of the way down you may not have
any brakes left.
Do not waiting until the last second to
engage the "brake's " ....
We as the OP live out West an as he stated we have a ton of
mountains and hills with long grades .....
Using the Tow Mode has worked well for me and many others
as long as you use it the proper way .....Going down a 6%
grade that is 14 miles long at 60mph with a 4,5, or 6 thousand
pound trailer or more then throwing it into tow mode and hitting
the brakes hard is the fools way of driving
......be safe