if you are a native speaker, i think a review of OG ,followed by the tests on Powerprep should give you enough practice.
is much much tougher. But it wont hurt to practice. Dont worry about the scores on Kaplan
Also, if you can, you can go through the different types of problems here. The problems might be tougher, but study them and post your solutions. For every mistake you make, write it down somewhere. Go over this list every time you start your preparation. you will see a marked improvement in your performance. of course, how you do you on test day totally depends on how much you can concentrate and keep your cool.