I've noticed that I have some severe lag with some specific ballparks. Fenway was bad, for example. When I come across one, I just copy the unmodded ballpark out of my clean MVP 2005 install and it runs smoothly. I know in the Total Classics mod, some of the parks are completely unplayable for me, especially old Yankee Stadium. I've tried the 4GB patch too. I think our systems just can't handle the bulkier modded stadiums.