I have been around it twice, both time clock wise. First time in a 36' MH and the second with a 40' MH, both time with a tow.
The 11% to 15% grades are very short, usually less than a quarter mile. They occur when the road leaves the coast line, goes inland over a hill, this drops back to the coast line. I did not find any of them a problem because they were so short.
There is a 17% grade entering Perce. It is about a half mile going up and a half mile going down. The only grade I found to be a problem was the one going down into Perce because it ends as you enter town and you are right at the main drag. You don't really have any time to slow down at the bottom of the grade so have to be going slow in the descent.
Thousands of people travel this road so take the trip and enjoy.