I had a similar experience. I was scoring 650, 660, and 680 in my last 3 practice tests, and then I took the test this past Sat. and scored a 530. I was so mad. I too thought the verbal was a killer (V28). The questions were tough right out of the gate. I messed up on the quant by getting hung up on a couple questions. I'm working on taking the test again in about 6 weeks. Here's my plan for studying:
1. Work on practice tests and questions other than OG and Prince Review
2. Work on my pacing and timing.
3. Create an error log
so I can review my weaknesses
Good luck on the second time around! I'm looking at McCombs too.