GMAT Strategy

I took the GMAT back in June and scored a ridiculous 390.....Now right then and there I should of given up and took up a construction job. On the long way home, I decided to really buckle down and give it my all. I gathered up all the bibles of reference (OG 10, OG 11, MGMAT SC, and all 1000 Series). I don't have the exact scoring for my practice but I've taken practice exams each weekend for the past 8 weeks. Scores ranging from 450 to 610. I seem to be in the range of 560-580. I recently took a GMAT prep and got a 510 (which was actually good because I spent a total week on Quant (NO VERBAL) and raised my Q to a 39 and in review of the wrong questions I had silly errors that would enhance my score).

The question I pose to the forum is I have about a month left and my goal is to get a 640, at least over a 600. What steps should I take (ie, new books or strategies) in order to move toward my goal?

Thanks again in advance.....