Can you tell me the math and verbal breakdown on your practice tests? Because of the difference in your two scores on the official test, I'm assuming that verbal drops a lot. Does math drop too, or is that about what you get on your practice tests?
As mg mentioned, anxiety can certainly cause problems on test day. You may want to read this article and see whether any of the techniques in here can help you:
http://www.manhattangmat.com/strategy-series-stress.cfm
Did you take your practice tests under full official conditions? (30m each for two essays, 10m break, 75m quant, 10m break, 75m verbal)
How was your timing in the each section? Did you generally move steadily through the test, giving appropriate time and attention to each question? (2 min for quant, 1 to 1.5m for SC, 2m for CR, 2-4m to read a passage, 1m for general RC questions, 2m for specific RC questions) Or did you have to rush at times and possibly make random guesses? If you did have to rush and/or make random guesses, on how many questions would you say you did that? Did you do it on a lot of questions in a row or were the guesses scattered?
How was your stamina? How did you feel toward the middle and end of the verbal section? Did you have something to eat and drink on the breaks? Did you get up, walk around, and stretch?
Besides the anxiety because you knew it was a real test, what other differences can you think of between your practice test experiences and your real test experiences? Anything, no matter how small, and no matter whether you think it wouldn't have made a difference to your score. Any differences at all?