Have you considered taking a class? It sounds like there are some elements of the test you are struggling with. I used Manhattan GMAT
and found it to be very helpful. Not only did they do a good job of teaching and testing concepts in a slightly more dynamic way than the books presented them, but it was helpful to be in a class with other bright people who were asking good questions.
A number of the test prep services offer online courses you can take from home. I would recommend looking into one. It may be able to accelerate your learning.