Devasting GMAT score

Hi everyone,

I have been preparing for GMAT for more than a year but continue to struggle to make progress especially in the verbal section. After months of preparation on the bus to work, in the breaks at work, I took my GMAT two days ago and scored a disappointing 510 Q41 V20. I could not believe the score because I was expecting to break at V30 or 600 (my highest so far is 560 Q42 V24 but scoring has been going down hill). I have taken plenty of practice tests and scored on average 620-670. But I don't seem to translate my ability to the real test. I am seeking help because I feel lost in this standardized test prep. My realistic target score is 660 Q45 V34 and am willing to give another try in another month or two. Can somebody recommend what resources to use? How can I identify and target my weakness? I want to know a good process to improve. I can even send the assessment report for my Manhattan CAT to help anyone understand where I stand. I have been thinking about tutor but don't know if that's right move. I have Manhattan books and e-GMAT subscription that I can definitely review more thoroughly. I appreciate your thought and comment. Thanks!

Michael