Sudden performance degradation

I'm using D3 connected to Access 97 via BDE 4.50.

This was working fine until (i think) my application got a bit big.

All of a sudden, the latest form I've created is painting/running incredibly
slowly.  It seems to be the database access which is really causing the
problem as disabling the filter in the Activate event on the form spped up
painting, but then navigating the records is slow.  If I set the filter on
Activate, the painting slows down.

What's weird is that the other forms (which use similar techniques) work

I ran just the form, datamodule etc from a new application, leaving out the
rest of the app and it runs quickly and perfectly.

Does anybody have any suggestions?