Endpoint Protection and Outlook attachements

I have recently installed Symantec Endpoint protection (12.1.671.4971) on a client computer (Win 7) that previously had Trend Micro (Dell OEM) installed. Since the install we seem to be experiencing very slow performance with Outlook and opening attachements, especially PDF's.

I've tried disabling Outlook Auto protect in virus and spyware protection settings and that seemed to speed things up again until I turned it back on again, which is what I want it to be able to do for security on that client.

Can anyone offer any suggestions?

Thanks

Mark