Horrible Performance for my machine

I am running on an intel 3770k, 12 gigs of ddr3 1600, and an AMD 7970 3 gig card, yet I get framerate drops that go down to around 20fps with a decent amount of things on the screen, from a strangely low 60ish average before a round starts.  The game does seem to eat some cpu power, but my processor is quite high spec, and the rest of my machine is equally so.  I can run almost any other game maxed out with a perfectly smooth framerate on my machine, yet for some reason Orcs Must Die 2 has managed to acheive the lowest framerate on any game I have played on this machine.  Any known issues, or fixes for this issue are greatly appreciated.