There are other resources available for SC and RC improvement. I suggest taking a look at the PowerScore series. The company has a strong reputation in the LSAT business, which is a test taken by law school candidates. The LSAT is mainly about verbal, so their guides should cover this section nicely. I myself used their CR Bible and found it to be a great resource for both CR and RC (after all, RC is CR with simpler questions but longer passages).

Also, improving RC and SC might require you to work on your general English. You'll often see posts recommending that you read as much high quality material as you possibly can: books, newspapers... You could also try buying a general grammar book (published by reputed companies such as Longman or Oxford) if you feel your SC isn't improving.