Kup, that is a HUGE jump, way to go!! I am so glad to see that you guys found my advice to be helpful!
As far as LR goes, I think that it is one of the toughest sections to obtain a big score improvement on. When I took my cold diagnostic test, my best LR section was a -7. As of now, I can score around -2 most of the time, but I still have some sections where I miss 5-7 questions, so the consistency is not perfect. I don't know how many specific points of advice I can give you for improving it, but let me relay my experience with LR and see if it can provide some insight:
I have approached every section in roughly the same way throughout my prep. I spent the first 8 weeks concentrating on learning the sections and question types as thoroughly as possible while focusing on untimed practice sections/tests to cement my understanding of the concepts. From the initial -7 and -13 on the LR sections of my diagnostic test, I got to a point where I was consistently hitting -2 to -4 max on my untimed LR sections.
One of the keys that I found to improving your untimed score is to track your performance and identify strengths and weaknesses in your game, and work on eliminating those weaknesses. In untimed sections, obviously your timing is not a major weakness you should worry about. Focus on identifying question types that you seem to consistently miss or take a really long time to answer, then take extra time to review those questions. Refer back to the LR Bible if you're not understanding something. Come here to the forum and look up the admins explanations for the questions you missed, then write out your own explanation in a way that you understand it. The big point here is to make sure you understand WHY you missed what you missed and develop a personal strategy to avoid such mistakes next time. You may not always successfully apply those strategies, or you may get tripped up here or there by a situation that you are unfamiliar with, but if you are understanding what you are doing wrong and consciously work hard to correct your mistakes, your score should improve over time.
Getting great scores on your untimed work will feel good and increase your confidence, but it doesn't mean much if you can't get it done in 35 minutes! So after I hit a comfortable level of mastery in untimed LR sections, introducing timing was the next step. Fortunately, I believe that getting the timing nailed is easier on LR than on any other section. I already laid out the strategy to develop timing in my last post as I have used the same "progressive trimming" technique on all of my sections. Something I will note about introducing timing though is that my score did drop off pretty considerably when I first started it, which can certainly be discouraging. However, as I got more comfortable going at a faster pace, I did not feel as though I had to rush through the questions. I simply got used to thinking faster and relying more on the intuitive understanding of the questions that I developed over the course of my untimed work, and my scores quickly caught up. The key is to introduce timing slowly in a way that will allow you to assimilate comfortably.
If you feel like you are plateauing in your scores, there is likely something going wrong. Sometimes it is just a matter of patience: I have had several times throughout my prep when I felt like my scores were going nowhere for a week or two, then all of a sudden I made a quantum leap forward into a new and improved score range. So if you haven't been stalled for that long, you may be fixing for a similar big jump! If it has been more of a persistent problem, you need to go back and find out where and why you are weak. If you started adding time pressure before you had an adequately strong understanding of the section, you may need to take a step back and do some more untimed work to cement your understanding. If you had a good understanding and were scoring well in untimed work but are consistently having trouble with the clock involved, you are likely forgetting things that were important to your previous success as a result of the clock. Go through the questions that you missed and try to find a trend. Evaluate what you did right and what you did not that you know you should have. If you are capable of scoring well without timing, you are capable of scoring just as well with it. You need to know that and just work on bringing the full package together for test day!
I hope you find some of this valuable. Again, what an awesome jump on your RC section! If you can do that for RC, I'm sure you can do the same on LR. You just need a plan to do it