Truckers rule of thumb, whatever fear it takes to go up, use the same gear coming down.
As for me, while towing, or heavy load, I watch the speed limit. I want to be 10 under, let it climb to the limit, then get the brakes, and get to 10 under. Let off the brakes and let it climb, then on the brakes. As long as you off the brakes as long as you on them, you will be fine. If you are on the brakes longer, then drop a gear. Also on some engines, have to watch the revs. Works for me, your mileage may vary.
Let me clarify. Some mountain roads I tow in are unmarked, so speed limit 55 mph. I ride a motorcycle that won't do 55 on some of them. Find a target MAX speed, and when you get there, get the brakes and drop 10 or more mph, then let off the brakes until target speed reaches again, the brake, then off, and so on. The idea is to give the brakes a chance to cool some. Hope this makes sense, getting late.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT