GTA IV Performance Issues [HELP]

Hi there, Im having performance issues on gta 4

Im using ENB series L3EVO87 but even before using the enb mod i was getting low fps on maxed out settings
Ive noticed that even on maxed out settings the game just uses 922MB of 1000MB

Heres my rig

AMD Phenom II x4 955 BE 3.8GHZ OC with Cooler Master Hyper 212+
XFX HD 6870 Dual Fan 970/1180 OC
Patriot Signature Line 8GB ( 2x4GB ) Stock
Samsung spinpoint f3 1TB 7200RPM 32 MB Cache
OCZ Fatal1ty 550W
Thermaltake v4 Black Edition Case

without enb and no mods i get good fps on auto settings, but if i max out the game, they drop like hell....
with enb and mods i get less fps in both cases

What shall i do to boost fps in GTA IV??

I can run this game easily with my rig......

I believe draw distance is a very intensive setting.

Draw distance isnt that high, its at 31 really.......

hmm, swapped road textures and it working relatively fine now......