Following this topic post helped me resolve the same issue you’re having. I’m not saying that it’s definitely the solution, but maybe something that you can try and see if it makes a difference. My spec is i9-9900K, RTX 2080 Ti, and 32 GB RAM. My sim was limited by mainthread and it was running at around 10 fps all around. Once I tweaked my BIOS according to this post, I got 30 FPS from that point on.