I've been stuck in the low 160s for months--since August actually. I kept drilling and scored a 163 on my November exam. I took a month off before getting back on the LSAT train, and I scored this after not touching the LSAT for a month. Praise God!
For those who remain in a plateau: Keep going. It will eventually click.

I didn't find the CC in general the most helpful. I needed a tutor to break down the lessons to me. 20 hours later, I feel pretty good about most-things LSAT. It may be my particular learning style. To answer your specific question, if I remember correctly, the grammar lessons are one of the first topics covered, so I tried to force myself through it. I found myself skipping most of the content toward the end as it was not the most engaging.
I agree with another poster that the grammar aspect of this exam, I think, it best learned through exposure.
Not sure if this is under the grammar section, but I refer to the conditional diagraming cheat sheet often.