Running out of materials to use

Hi guys,
So I've taken the GMAT 4 times already, with the highest score only being 620. I know that I can do better! But I've exhausted almost all the material out there...I"ve gone through OG twice, both Kaplan books and most of PR. My problem is that I've got almost all the questions memorized and it's hard to really analyze and learn from them (especially on the CD-rom practice tests). I've thought about getting a tutor but they are really expensive. The only other books that I haven't tired yet are the Manhattan GMAT books....any one have any opinon on them or any advice? I'm running out of steam and patience but I know that I can break the 700 barrier.

thanks!