Hi jhshin2,
At higher score levels, the GMAT becomes really sensitive to silly/little mistakes - with a 750+ score goal, you do NOT have a lot of 'wiggle room' for mistakes. You also have to be careful to train for the specifics of Test Day (take the FULL CAT, away from your home, at the same time of day as your Official GMAT, etc.).
1) When you reviewed this last CAT, how many questions did you get wrong that you COULD have gotten correct (but you made a silly/little mistake)?
2) How many of the Verbal questions did you 'narrow down to 2 choices, but still get wrong?'
3) How many questions were just too hard?
While you're asking about free CATs, taking lots of CATs is NOT what will make you a better Test Taker - that improvement will come from learning the necessary content and Tactics, and then practicing enough for them to become a natural part of your way of dealing with the GMAT.
GMAT assassins aren't born, they're made,
Rich