If you were going up in 2nd gear, you should have kept it in 2nd on the way down, and at the same speed. As most people would, you probably started to speed up cresting the pass, and were just going to fast to begin the decent. Everyone does it until they experience the brake fade you mentioned, then they change the way they drive.
Boosting the trailer brakes may have worked this time, but just imagine what would have happened if they failed!
We are never in such a rush that we can't take an extra 5 minutes to make a safe decent.
I have been on many of Colorado's mountain highways, and have always been extra cautious. And most other drivers realise the danger, and seldom give you a hard time for driving slower.