Strange frame drops

[HEL(L)ICOPRION]

Hi all,
it's not the first time that i play graw 2, but it's been a while since the last time..so i've reinstalled it a couple of days ago and i've noticed that the game it's nearly unplayable due to huge frame drops, apparently random...i thought that was some dirver related issue, so i've done a clear reinstallation of it, but with no luck, i still have the same problem...
Now, i've always played this game maxed out with smooth fps...and i havent' changed my rig either since then (so i would prefer to find a solution without lowering my ingame graphic settings)...i've just went from vista to seven...do somebody know if there's a way to fix this?...tnx