I'm sorry you had a disappointing test experience. It could be that you burned yourself out, yes - it's not a good idea to cram for this test. You could also have timing problems, you could have been suffering from mental fatigue, your practice test scores could have been inflated... there are all kinds of reasons why.
It's also the case that these tests have standard deviations - and your score drop is within the standard deviation expected for our own tests, though a little bit more than expected for GMATPrep.
Did you take your practice tests under 100% official conditions,
including essay and IR? Did you do the essay and IR sections as seriously as you did on the real test? Did you limit yourself to two 8-minute breaks? Etc. If you gave yourself any leeway on practice tests that you don't get on the real test, then your practice scores might have been artificially inflated.
I have already done the GMAT book (13 edition) twice and I know most of the questions by now. Same with MGMAT and GMAT PREP exams.
As you'll learn if you read my posts around here, just because you've done the problems, and just because you know the answers, that doesn't mean you're necessarily done *studying* those problems.
Read this and pay particular attention to the How to Study portions of the second half:
http://www.manhattangmat.com/blog/index ... an-part-1/http://www.manhattangmat.com/blog/index ... an-part-2/Were you learning in that way? Or is there room for you to do better?
How was your timing? It's very difficult to score 720+ if you have even minor timing problems (and just finishing the sections on time does not mean that you don't have timing problems!). Read these:
http://www.manhattangmat.com/blog/index ... to-win-it/http://www.manhattangmat.com/blog/index ... nt-part-1/Take a look at this for other ideas about why your score may have dropped:
http://www.manhattangmat.com/blog/index ... ent-wrong/Then come back here and answer all of my questions above. Also, use the below to analyze your most recent MGMAT CAT(s):
http://www.manhattangmat.com/blog/index ... ice-tests/Then come back here and tell us the results of your analysis and what you think you should do based on that analysis. (Note: do share an analysis with us, not just the raw data. Part of getting better is developing your ability to analyze your results - figure out what they mean and what you think you should do about them!)