I've been having an irritating issue with Gta iv (EFLC) recently. I can play the game normally, but after 20+ minutes of play the game freezes for a few seconds, then resumes, but all the floor, building etc. textures disappear completely. I have no car mods installed, i use only the default models and textures. I have some script mods running in the game, but they shouldn't be causing this. I have only had this recently, but i haven't changed any models. I changed my Commandline options to see if that did anything, but nothing changes. I think that my 32-bit system may be limiting the memory EFLC uses, but im going to upgrade to 64-bit soon. 

 

Specs:

OS: Windows 7 32-bit

RAM: 8GB

CPU: AMD FX- 4170 Quad-core @4GHZ

GPU: AMD Radeon 6670 2GB

 

Script Mods:

LCPDFR 1.0b

Policehelper script

IVdashcam

Breathalyser script

Firstperson script

Trainer

Coroner script

Tow truck script

 

I don't know much about AMD cards so I can't help there but I know for a fact your 32-bit copy of Windows 7 is part of the problem. You have more than capable RAM, but a 32-bit OS limits you on how much RAM processes, such as games, can use. GTA IV is prone to memory leaks and is a very demanding game, so I'd suggest upgrading to a 64-bit OS. I can't guarantee upgrading will rule out the issue completely, but it'll certainly make it less prominent. 

Post all your .img file sizes in your "pc/models/cdimages"