This game really pisses me off

i have tried last 3 weeks to correct that texture loading problem...like using commandline,game booster,cache booster, CCcleaner, cache cleaner, lowering graphic settings, loading new drivers to my video card, Loading older drivers, Loaded car packs, uninstalled car packs, uninstalling game. fresh install to game and none of these methods are working. if someone dont know the problem allready i will give u a little description. i start the game averything is fine like 10 mins then textures start to load very slow and that makes the game unplayable. Does anyone know any good method to prevent this to happen if so PLS tell me!! My system specs are here
Windows 7 64 bit
AMD athlon Triple core pros
6gb ram
Nvidia Gforce GT320 1042mb
The game is newest version 1.0.7 or what ever and its Steam version
THX for advance.....i hope somebody has some good advice to give or i will forget this game.