I hate to say it, but it sounds an awful lot like you have a split file. It has gotten so big that part has broken off, and sometimes one part is accessed for scoring, and sometimes the other part. This can happen if you have a zillion accounts, and it can also happen if you pull your reports and scores a lot--the soft inquiries are taking up too much room.
Print off one report with the lower score and another with the higher, and do a line by line comparison of the two. If the file is split, something is bound to be different in your list of accounts, or the info for the accounts.
If the two files don't match, you'll need to call Equifax. It's a PITA, and it can take several weeks to fix (or one day), but you need to get the thing glued back together again. Try to find an old printed report that has all the accounts on it. Good luck!
* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit?
FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007