It's taken me years but I finally get the Rest Step. I feel silly that it took me so long to get it but it involves immediately locking your knee and I've been conditioned for years to not lock my knees so it was a huge mental and physical block for me.
When you take a step you straighten and lock the leg that is getting the weight (what will become the trailing leg) and relax the leg that is brought forward for the next step. The thing I wasn't getting is that you straighten and lock the leg immediately. In this way, you can walk uphill at nearly normal speed.
I was hoping I could find a You Tube video on The [Mountaineering] Rest Step but there isn't one (and there needs to be one).
There are these refs:
From Mountaineering: The Freedom of the Hills
I finally put it together while working out at the gym with a pack. It became clear even before I got to the stair climber machine but when I was walking up the real stairs of the gym. I hit a rhythm and was able to then work out on the stair climber for 45 minutes while carrying a 27.5 lb pack. It of course helped that NCAA Women's Fast Pitch Softball championships were on as I'm real familiar with fast pitch softball as I spent all of jr high and high school playing softball until I had to quit from a shoulder injury which I handled all wrong so it didn't heal for years. (As a result I became an excellent hitter.)
I walked out of the gym knowing that, for once, I was ready for Shasta. I should increase the weight and the speed but I pretty much have it.