Well, folks, I have towed on the 26 percent grade at Sonora Pass, both up and down, no problem. I first got clearance from a law enforcement officer at a local office that I will not name. My truck is 16 feet long, and so is my trailer (coupler to bumper). The officer told me that the combination should be fine on that grade and those turns.
The officer was right. I stayed in my lane the whole time, and had no trouble pulling up, and no trouble coming down. We boondocked for a week up at the pass -- heaven on earth, at 9500 feet.
Don't try this in anything larger, though! We saw an accident involving a commercial trailer -- nobody hurt, but a lot of vehicle damage.
By comparison, Tioga is a piece of cake -- excellent pullouts, and plenty of them. Eight percent.