Hi cocojatti92,
Retaking a CAT that you've already taken will likely lead to seeing 'repeat' questions. Unfortunately, seeing even a few questions that you've already faced will throw off the Score Algorithm and the 'realism' of the experience (your pacing, stress and energy levels will all be 'better' than they normally would be). To properly assess your skills, strengths and weaknesses, you shouldn't take CATs in that way. From your question, I assume that you've taken the Exam Pack 1 CATs (re: CATs 3 and 4) before - so you shouldn't buy them again. If you need some new practice CATs, then there are some reputable 3rd-party CATs that you can use.
Before I can offer you any additional advice, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How long have you studied?
2) What study materials have you used so far?
3) How have you scored on EACH of your CATs (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
4) What is your goal score?
5) When are you planning to take the GMAT?
6) When are you planning to apply to Business School?
7) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich