Hi manomoyc,
The scoring algorithm on the Official GMAT is far more complicated than most people realize. Since that algorithm is proprietary, no GMAT company has an exact match for it, thus CAT scores can vary a bit based on the 'biases' involved in their respective designs. The most realistic CATs available are the 6 from GMAC, but the CATs from Kaplan,
MGMAT and Veritas are all 'close enough' to the real thing that they will provide you with a relatively realistic score assessment (assuming that you correctly take the CAT in a realistic fashion).
At higher-and-higher score levels, the GMAT becomes really 'sensitive' to little mistakes (especially on 'gettable' questions). Thus, you also have to be detailed about how you performed on each of these CATs. How many questions did you get wrong because of silly/little mistakes? If you're missing out on too many gettable points, then the accuracy of the CAT isn't the issue - the work that you did (or didn't do) during that CAT is what you have to be concerned with.
Before I can offer you any additional advice, it would help if you could provide a bit more information on how you've been studying and your goals:
1) How long have you studied?
2) What study materials have you used so far?
3) When are you planning to apply to Business School?
4) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich