I actually started down some of the descents the other night in reverse. There was no question where the traction was, or wasn't. Ice looks like ice, you can't miss it. I also kept 1 foot on the gas, 1 foot on the brake and my hand on the E-brake.
Clearly, this is a last resort and a sketchy technique that claimed MtnAddict's ring gear on the way down. I was more concerned with getting sideways and rolling over with my wife and kids in the truck. I can't stress enough how out of control that ice filled descent was. There was no/none/zero traction on the way down.
Once you get to a certain speed, staying on a tight trail like that was out of the question. If you're on full ice like we were, the reverse/brake/gas/e brake can help you at least stay straight.