Well CalTrans has that section of Sonora Pass posted 28% and I can tell you with a big camper it is a grunt but not too long. The main thing is if you are climbing it make your gear selection (manual) ahead of time because if you decide to change gears while climbing you are going to be at a near dead stop before you finish the change.
I have climbed a steeper one but it was short, on the way to Trinity Lake. It had the added attraction of going around a sharp curve and besides the TC I had a boat. It was a second gear climb and that was when I had my motor pumped an extra 150 hp and on diesel not biodiesel.