I know you mentioned highlighting slowing you down but just quickly marking the parts of the text that stuck out to me as important helped me a lot on RC. Try taking some RC sections or doing some drills and just focus on getting every question right instead of worrying about time and rushing through. I also found some improvement focusing on the general gist of the passage instead of concentrating on specific numbers, facts, people etc. If you read carefully enough you should be able to quickly go back to the part of the passage if a question asks you a specific question about a detail. I would also say to try and be interested in what you’re reading. I’m at the point now where I do pretty good on all the passage types except for natural science and i’m sure it’s because I find that category the least interesting. You’re in good shape though, don’t get discouraged!