Logic Pro 8 Audio CPU Overload

I have moved my sample libraries from an internal 7200 Maxtor drive to an external GRaid 2 drive and finding that songs that previously ran ok are now gliching due to Core Audio system overload . The audio cpu is maxing out on the right channel . disk I/O ok . The G tech drive is connected via firewire 800 Have tried 2nd cable , same problem. Any help suggestions ?
thanks from a new member