Not to slam the Kaplan materials, but from my limited experience with them, it seemed like they were focused more on gimmicks (e.g., back solving, picking numbers) than on actual problem-solving strategies. I would strongly recommend the
MGMAT strategy guides for quant. From what I understand, the
MGMAT SC guide is also one of the best guides around for that topic.
Going back to a point emont made earlier, why the rush to take the GMAT and go to business school? Unless an employer is requiring you to get an MBA to "check the box" for some reason, it probably makes sense to wait a few years, and apply to more highly ranked schools. If you can combine a strong GMAT with a 3.6 GPA, it seems that you could do better. I'm not trying to tell you what to do with your life, but getting an MBA is not inexpensive, and you should be clear on your motivation for doing so. I would strongly advise taking your time with the GMAT, learning core concepts, and revising your business school choices based on the results. Best of luck.