I struggled through Jim's book when I was studying drums at 17. I had to chart it all out: FLR-FRL-FF-FLR, etc. That was the only way I could get it, and I never really mastered it, I must admit. Years later, when I got to know Jim well, I told him what trouble I had with the book, and he replied, "Good! It was meant to be difficult, but it made you a better drummer, didn't it?" It did in the long run.
I found that Jim's book translated also to the rock stuff I played, although it was meant to be a jazz study.