https://gmatclub.com/forum/compiled-thu ... 54538.htmlhere is a link to post on this forum which has videos of thursdays with ron, or you can download Vimeo and watch on that.
As you said, you have knowledge of theory but application is problem.It might be fact that some you are able to identify the issues, but struggling in hard problems. Please note, that each SC ques, doesn't has just 1 option to make it wrong, Its wrong in many ways,
You should follow strategy to bring down from 5 to 2 or 3 options, and then see what's wrong in that. If you are already doing it, Please see your
error log, if any option you have done WRONG, why you thought that was correct and why RIGHT was right. It will lead you to see GMAT traps in hard questions. Further analyse various grammatical errors in single problem, it will just open your ways to eliminate wrong problems more strongly.
All the best