Hi dml,
Since your practice CAT scores are consistently higher than your Official Scores, something is clearly "off" in how you're practicing or in how you're facing Test Day (or both).
I have a few questions about how you took your CATs:
1) What "brand" of CATs did you use?
2) Did you take the ENTIRE CAT each time (including the Essay and IR sections)?
3) What time of day did you take your CATs and what time of day was your Official GMAT?
4) Do you take your CATs at home or do you go to a different location?
5) Do you do anything during your CATs that is not 'test-like' (skipping sections, pausing the CAT, listening to music, etc.)?
6) How long is the ride to the Testing Center from your home?
7) On the Official GMAT, do you have to rush to finish any of the sections (and guess on a bunch of questions just to finish)? Do you finish any of the sections early?
Thankfully, the GMAT is a predictable, standardized Test, so you CAN train to score at a higher level.
GMAT assassins aren't born, they're made,
Rich