I keep consistently getting 730s in CR and the questions that I miss are usually 2 vocabs and 3 passage based.
To a certain point, how can one improve his/her score further? I’m not sure what to do anymore except memorize large vocab lists.
I’m not sure how much this helps, but I’ve had it bookmarked and I’m sure it’s worth a read: http://ultimatesatverbal.blogspot.com/p/how-to-study-for-sat-critical-reading.html
Maybe you can try switching up your passage reading technique? I found that breaking it up into small chunks and taking it question by question really helped.
Anyways, if you make sure you don’t miss any vocab, 3 wrong should get you a 780+, which is already great.
Sorry I couldn’t be more helpful 
, passage reading is pretty tough to improve. Good luck!