I'm not sure if others are experiencing exactly the same issue as mine. I have a GTX1080 Ti and no matter what graphics preset I used (low, high, ultra), the game would stutter like as in drop in frame rate. I've tried adjusting the settings like turning off vsync, turning off motion blur, setting my nvidia control panel to max power preferred.. nothing worked. Until I remembered I used to have Razor Cortez (search for Razor Cortez game optimizer) and it had helped me in the past. So I installed it and it was NIGHT and DAY. There may still be some stutter occasionally, mostly I think because you've gone into a new area of the map and perhaps my SSD or CPU needed some time to load the new area but by and large, most of the constant annoying stutters are gone!!
I was so turned off by the constant stuttering I actually didn't play it after 20min and didn't come back to it until a month later. Now, I am having a blast. Also, I have the preset turned up to ultra and the game looks beautiful locked at 60fps.
Anyway, if you've tried everything (including setting the game to real time and removing CPU 0 from the affinity in task manager) and had no luck, give Razor Cortex a try.. hopefully this helps someone. Good luck!