Thanks guys for your suggestions. I'm towing with a 1995 Range Rover (rated at 7,400 lbs towing) and towing my 1994 Mac 26C on their trailer with the surge brakes. I understand the boat has been over the mountains in the past, and in the 20 years of age, the trailer brakes have been replaced once. (I'll get them checked before the over mountain trip).
My only Rover concern is the transmission that heats up when towing, even though it has a giant trans cooler radiator, but otherwise works just fine. I'll probably put in the
best Amsoil Tranny fluid before the over mtn trip.
Going down the mountain without trailer, on gear drop keeps it around the speed limit without riding the brakes, so will try 2 gears down with the trailer, and keep it gradual to minimize trailer brake pressure. I don't remember pull off places to check the brake heat going West, but appreciate all your input.