How can I up my score on 2ed GMAT Attempt?

If PS is what trips you up, chances are you will be better off re-learning the basics, rather than just trying to do a lot of practice tests. Kaplan, Princeton Review, and PowerPrep have math reviews; start there and then supplement with other sources - either online, or with old high school math textbooks, or whatever.

Try to target your studying to the areas where you have the most difficulty. For example, if you are missing a lot of geometry problems, maybe a geometry crash course is in order. If most of your mistakes seem to come on number properties questions, review your number properties and know them cold. If you're running out of time because you're slow at doing calculations without a calculator (like me), review some tips to get your speed up. Etcetera.

PS is the easiest section to see a vast improvement on in a short amount of time. That's the good news. So good luck!