The first thing to do is take at least one full week off from GMAT. You need a rest. Also, whenever you have time, read this thread:
should-i-retake-gmat-thread-retaking-gmat-strategies-83339.htmlYou have already identified one issue: test exhaustion. It happens to all of us to one degree or another. The best way to minimize this condition is to always practice questions and take CAT's under the exact same conditions as you would for the real test. Don't practice OG on the sofa, for instance. Sit in the computer chair and use a desk. You can even prop up the book vertically to mimic the computer screen. It's also important to use a timer. For CAT's, follow the time limits and breaks exactly. People who don't do these simple procedures are only cheating themselves out of points.
It's equally important to take advantage of the breaks. Take that time to walk around, stretch, splash cold water on your face, and eat something (Snickers, almonds, a banana, Gatorade, etc.). I also find it helpful to look away from the screen and take a deep breath every time a new question appeared on the screen. This reduces neck and eye strain and provides oxygen. You need to maximize your energy reserves because you will definitely begin to run out toward the end.
But now to the books and CAT's. I usually urge others to be conservative with the GMATPrep because those simulations tend to inflate scores after the second time. And the AWA must be included in your tests to practice essays under timed conditions and to get used to taking the entire test. This was probably one reason why you broke down toward the end; you weren't fully conditioned to go through all three sections of the test. This cost you points - points that you already had.
Besides the Manhattan SC, I don't see any other proper guidebooks for verbal. You're quant skills are superb, so we probably don't have to worry about that. Right now, let's focus on verbal.
SENTENCE CORRECTION (SC):Read the Manhattan SC guide at least one more time. Re-reading is one of the best things that you can do for studying.
CRITICAL REASONING (CR):The Powerscore CR Bible is the best GMAT guidebook on this topic. This is a must.
READING COMPREHENSION (RC):Start practicing with LSAT RC passages. These are generally more difficult and complex, so they will build up your stamina. If RC is your weak point, then consider a Powerscore or
MGMAT RC guidebook.
While you are improving your verbal skills, go ahead and use the
GMATClub Tests to retain you high quant score. Among other things, these tests will definitely strengthen your endurance. Also, if you haven't done so, go ahead and purchase the OG Verbal.