Weird graphics lighting glitch and FPS drop

Just got the game a week ago thru Steam, and I haven’t been able to get it to run smoothly, and also have strange brightness/lighting glitches.

Firstly, my rig should be able to run this thing on ultra or at least high:

i5 6600k (unclocked)

16gb ram

1080ti

1440p gsync monitor

Windows 7 (maybe the issue?)

1st problem: FPS drops

The game keeps dropping from 45-60 regularly to chugging around 15 for a bit, until it jumps back up again. Doesn’t matter what I’m doing, in fact mostly it occurs when I’ve just unpaused or even if I’m just in the garage. Gfx settings have no effect, it still does it on low, and 1080p.

Additionally, I get smaller FPS drops while cornering or when there’s a lot of effects on screen (like when a race begins), which seems more like normal performance load stuff, but again gfx settings don’t seem to help so I think it’s related to the other FPS issue.

2nd problem: glitched lighting

And finally, I have a weird lighting issue where certain things will for some reason get super saturated with colour and brightness, to the point that neon rain sometimes blinds me at night. Or about 1/3 of trees will be weirdly bright green, while the rest looks normal. Same thing happened in a shipping yard: some shipping boxes were weirdly bright, like they were their own light source, while most looked normal.

I managed to capture a shot showing these strangely bright trees. It's a day shot, btw.

As I said I’ve tried lowering every gfx setting, performance stays the same. I’ve tried various optimization including power settings, Nvidia settings and creating a user.cfg file in the game directory (to tell the game to properly utilize my 4 cpu cores, apparently). I’ve tried closing every other app. I’ve reinstalled Nvidia drivers. I’m not sure what else to try.

Has anyone else experienced issues like these with this game? If so, wtf did you do to fix it??

Thx!