Need advice for towing downhill....

Also remember that the speed of your descent should not be faster than your climb. When going down the hill, try to find a speed that allows the engine to hold your speed with corrections done by short braking. If you have to brake heavily, you are going too fast.

A few weeks ago when in Lake Placid, we decided to drive up Whiteface Mountain. There are signs all the way down advising people to use engine breaks on the decent. According to one of the staff I was talking to in the summit parking lot, someone decided to ignore that and their breaks caught fire part way down the mountain. I took it in first or second the whole way down and only had to tap on the breaks a few times coming into a few hair pins going down the switchback.
long descent + engine breaks = good
long descent + regular breaks = bad

Tranny yes. Then brake for only a moment to slow down the revving of the engine and let off the brakes so they will not over heat,

Definitely use tranny. Not hard on it at all.