I can relate to your SC frustrations - I've been working on SC exclusively for about two weeks, and I've made some progress. Here are some tips that I found useful:
- Despite what people tell you, the Kaplan books aren't terrible. They are extremely structured and will help you identify the typical types of errors. While the types of questions don't really reflect the OG questions; once you're finished with the book you'll be able to really easily when you see 'verb form' errors or 'parallel structure' errors.
- Once I started to hit my 'typical errors' at about an 80% hit rate on OG. I started to better understand the 'GMAT Voice' (typically this when the solutions identify solutions as 'awkward and wordy')
Please let me know if you make any progress, or learn any tips. SC questions have been ruining my GMAT test scores too.