How often are you taking these CATs? They should be so far apart that you could re-do them (because you're forgetting most of the questions).
Practice CATs are really good for (a) figuring out where you're scoring right now, (b) practicing stamina, and (c) analyzing your strengths and weaknesses. The actual act of just taking the exam is NOT so useful for improving. It's what you do with the test results / between tests that helps you to improve. You should be able to get a *minimum* of 1 week's worth of study out of a CAT (and more typically 2-4 weeks).
So if you're taking CATs really frequently because you think that's how you're improving... well, let's just say that that's a very inefficient way to study. :) If you haven't taken that last one yet, DON'T. Use this to analyze the test:
http://www.manhattangmat.com/blog/index ... ice-tests/And look at the "how to study / learn" section here for what to do with those test results:
http://www.manhattangmat.com/blog/index ... -the-gmat/If, on the other hand, you just have a really good memory and so, unusually, you're remembering many of the questions, then yes, you'll need something else. Have you also already done the two GMATPrep exams? You could also try 800Score. (But I think GMATPrep and our CATs are really the best - which is another reason why you don't want to waste them.)
Finally, are you taking these exams under 100% official conditions? Including essay and IR? If not, make sure you're doing this - otherwise, you're really wasting the CATs.