How many tables do you have open?
What are your computer specs? CPU, RAM, hard disk size and space?
Have you defragged your hard disk recently? This can make huge difference.
Stop the postgres service (Start > Programs > Postgres > Stop Service) before you defrag so that the postgres database files can be defragged too.
Make sure you don't have any old hand history files left behind.
With Full Tilt stopped, open the FTP\Hand History folder and see if there are any old .tmp files. If there are, remove them. These should be removed by the FT software when you close the table, but sometimes some get left behind and if too many build up it can cause problems for PT3.
Make sure that your HUD options are set to reasonable values and aren't preventing the cache being used.
Tutorial: Configuring HUD Options