fps problem

Yesterday i played all day under 7.21 60 fps v-sync even in very late game heavy fight.

Today since 7.22 60 fps v-sync during game but when late game under heavy fight i have huge fps drop 40 fps and then when i dont fight, back to 60.. very playable but annoying and i dont think its my computer since like i said i played alot yesterday and i had no problem.

Anyone got the same thing? ( srry bad english )