GTA 4 Poor Performance

Hi there

I need help, i just picked up GTA 4 after installing te game im getting poor performance. I just can't get over 30 FPS i even tryed lowering my setting to low and it still doesn't help.

My Specs:

Playing in 1920x1080 With everything maxed

Intel i5 3570K (Ivy Bridge) Overclocked to 4.7GHz

Asus P8Z77-V LX Motherboard

2x Asus Radeon HD 6850 Crossfire

12GB of Ram

Corsair AX850M PSU

So my pc well exceeds the recommended specs i mean CPU usage 63%, System management usage 35%, Graphical usage 53% im not even pushing my pc, so why am i getting crappy FPS

I can play BF3 in 64 player lobby on ultra with about 100-120 FPS

It would be most appreciated if someone could help me out

Elliott