Santier...don't give up yet! First, ditch Princeton Review. I took the prep course and only improved 20 points from my written diagnostic. Plus, their Reading Comprehension techniques are pathetic.
Go out and buy Kaplan's GMAT 2004 w/CD-ROM. Also, get the Official GMAT Guide, if you don't have it yet.
Follow Kaplan's computerized lesson plan and supplement each computer lesson by doing questions from
the Official Guide. Make sure you spend a lot of time reading and understanding solutions from
the Official Guide. Try and do all questions if possible, but mix them up during your study plan.
When you say you're studying a lot, how much are you studying? I found 30 hrs/week appropriate for about 5 weeks leading up to the exam.
If you have more time than 5 weeks, start reading well-written novels for pleasure. It WILL improve your verbal score.
Good luck & don't give up! I know someone who's taken the GMAT 4 times and gotten into a top-5 school.