Hello and sorry about the issue!
Hmm, this is an odd case. There may be a number of things going on. If I may ask, can you run this software: User Bench Mark - and then paste the results URL here as a reply? It will help me diagnose what might be going on performance-wise.
Hopefully we can figure this one out soon so you can get back to playing some buttery-smooth CDitDZ action!
-Cheers