Seeking advice on retaking GMAT - focusing on verbal

I have taken the GMAT twice and am frustrated with the lack of improvement in between attempts despite the additional effort that has been put in. I don't want to believe that this is my plateau because some of my recent practice tests have been great (700-760 with verbal in the 35-40 and quant in the 46-51 range for my last 5 which gave me the confidence to do the second attempt that didn't turn out the way I wanted). I want to retake one more time for good measure because of the encouraging results from the practice tests. If anyone else had a similar experience or recommendations to overcome the 700 barrier, particularly in improving the verbal section...please help!!

March 2011 - 650 (47 Q, 33 V)
Study materials used: OG, Kaplan, Princeton Review

June 2011 - 640 (47 Q, 32 V)
Study materials used: Knewton Course, PowerScore Critical Reasoning Bible, Manhattan GMAT Sentence Correction

I'm going to admit that I was actually shocked with the second result given the improvements I had achieved in the practice tests. During exam day I had time management issues with the Quant section, but not the Verbal which further added to my surprise when I received the disappointing result.

I'm a female native English speaker with an engineering background from Canada and wish to apply to the top 15 (Wharton, CBS, Booth, Kellogg, Johnson) schools which is why I'm so persistent in trying to get to 700. I'd like to apply for round 1 in the fall which leaves me with little time. I'm also worried that even if I do get 700+ on my last attempt that the adcom may consider the last score a lucky score or a result of spending a year of my life on this which will make it look less impressive.

Please let me know your thoughts on how I should change my strategy or study plan to improve my score by September!