Framrate issue?

i have everything on the highest settings...and i run the test and it comes back good every time the refresh rate is at 60...matter fact the game is set to everything on the highest settings so im sure its not my computer being to slow or anything. Even if I set the game to its lowest settings it still has the kind of skipping and stuttering when heavy transitions. What could this problem be?

here are my computer specs

i5 quad core 2500k at 3.3 ghz
4GB ram
ati diamond 6850 hd

idk know what it can be...can you guys help me out?