Computer not running as fast as I think it should

Hi,
I have a Gateway FX8040 machine. Intel Core 2 Quad Processor Q6600
500 GB SATA II Hard Drive
4 Gigs of Ram
EVGA GTX 260 Video Card

I play many games on my machine and notice my performance isn't what I think it should be. After months of doing tests I think it might have to do with the DPC Latency. When I use the DPC latency checker, it says I have a constant 1000. I am not experiencing any audio dropouts. When I play for example World of Warcraft, my fps is great and a constant 60-75. When I get into a busy area or am in a raid, the fps drops significantly to about 10-15. After talking to several people, they think my computer should be able to run a lot faster than that. IS the DPC latency my problem? What should I do to fix it? I am leaning towards trying to find a new motherboard... I have all drivers up to date, I have reinstalled my OS, and I bought my new video card to see if my old video card was the problem (it wasn't). Any help would be greatly appreciated.
-Thanks!