Do not install traffic load and flow
These mods are for those who can't see vehicles on the roads. And you have better PC than I have. So it's strange. I will tell you what I did with my GTA. You should try this.
But before you do that try lowest settings (turn off shadows, min reflections, vehicle density at 20)
I have patch 1.0.4 coz it has no bug after installing Icenhancer (which improves grpahics) If you have patch 1.0.7 than you must live with red sky(after installing ICEnhancer) coz downgrapding doesn't work for the GTA.
INSTALL PATCH 1.0.4 (If you have 1.0.7 live with that)
Install this grpahic MOD
There is a readme file, you must copy everything from specyfic folder to the GTA IV FOLDER on your disk
After you do that go to the folder which is in that MOD. It's called settings (chose LOW and paste it to the main GTA IV FOLDER)
Take from here only the TIMECYC file and paste it where README file says
Then go to the main GTA iv folder and create a txt file (right mouse button,add note and name it COMMANDLINE)
Open "Commandline.txt"(that you have just created) and paste there this
Check GTA IV