GMAT Strategy

Hi Everyone, hope all is well. I can't seem to understand why, but my GMAT Prep diagnostic scores are always the lowest. I guess this is a bad sign, but I am not certain as to what is causing it. I don't think it has to do with doing the AWA or not doing the AWA because they seem to be uniformly worse.

Please see below:

GMAT Prep 1 2011-06-05
//620
MGMAT 2011-06-11
V31 Q45 //620
GMAT Prep 1 2011-06-17
V33 Q47 //640
GMAT Simulator 2011-06-19
V42 Q47 //700
MGMAT 2011-06-23
V33 Q41 //610
Veritas GMATLife2011-06-24
V39 Q47 //670
MGMAT 2011-06-30
V31 Q46 //650
Kaplan 2011-07-02
V34 Q44 //640
Veritas Simul 2011-07-03
V37 Q42 //640
MGMAT 2011-07-08
V41 Q43 //700
GMAT Prep 1 2011-07-09
//610
MGMAT 2011-07-15
V37 Q44 //670
MGMAT 2011-07-22
V39 Q43 //680
GMAT Prep 2 2011-07-24
V27 Q43 //580

The latest score is devastating, because I am planning to take the test next week - however, the score I got back was the worst I have ever achieved. I can see why, because I've gotten the last 7/8 questions wrong on the verbal section, causing a pathetic 27. I suppose it has to do with time management, and the fact that I did have to rushing through the last 10 questions or so.

Could that be the only reason? Or am I simply too optimistic?