Hi GMAT717,
Many GMATers become tired during the Verbal section of the GMAT, so you're not alone. However, based on what you described, it might be that you were not properly training for the FULL GMAT during your studies. When you took your practice CAT Tests, were you taking the FULL Test (with the Essay and IR sections)? If you were not, then you were actually taking shorter, easier practice Tests that required less effort and energy from you. By extension, you would not have been properly prepared to face the FULL GMAT on Test Day.
There are plenty of practice Exams available (for free or at a relatively low cost) - andy of the Official GMAC CATs or those offered by Kaplan,
MGMAT or Veritas would be fine. Just remember that you should take the FULL CAT so that we have a realistic score result to use as a basis for comparison.
GMAT assassins aren't born, they're made,
Rich