Hi arpshriv,
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, these 3 CAT score results show that you essentially performed the same each time (about 600 +/- a few points). Thus, it appears that regardless of what you've studied/learned, you continue to 'respond' to the Tests in the same general ways. Have you filled out a Mistake Tracker/CAT Analyzer for each of these CATs? If you email me the most recent one, then I'll be happy to review it for you and determine what you'll need to work on to improve.
GMAT assassins aren't born, they're made,
Rich