Hi carlosbarredac,
GMAC has publicly stated that the Official Score that you earn on Test Day is within +/- 30 points of actual ability. Assuming a similar 'swing' in how your CATs function, your 2 CAT score results show that you essentially performed the same each time (about 600 +/- a few Scaled Score points in each section). You handle certain aspects of the GMAT consistently well, but you also make certain consistent mistakes. With your current Test Date, you have about 7 weeks of study time remaining - and while you could potentially improve a great deal during that time - raising a 600 to 750+ during that stretch might be too difficult a task to be considered realistic (it would likely take at least another 3 months of consistent, guided study). By extension, you might need to change your plans a bit.
From what you've described, your studies so far have been 'book heavy.' Unfortunately, many Test Takers who use a book heavy study approach end up getting 'stuck' at a particular score level - and it's possible that this has happened to you as well. This is all meant to say that you might find it beneficial to invest in some new, non-book resources with an emphasis on Tactics.
1) Is your Score Goal still 750?
2) Going forward, how many hours can you consistently study each week?
GMAT assassins aren't born, they're made,
Rich