I am experiencing stutters as well, however for me these also happen in GTA itself.
I fixed the issue by enabling Vsync (60Hz for my monitor) in my case. As soon as I hit like 120 fps or more, these stutters will start randomly while the Steam fps counter still shows 120+ fps but it feels like playing with 10fps for a few seconds.
I never had that issue with my previous cpu where I only hit like 100 fps max.
Maybe vsync helps for your stutters. Though if your ram is getting maxed out, that would explain these stutters as well and then you can disregard my message 
Current setup:
Ryzen 7 5800x (16x 3.8GHz)
GTX 1080 8GB (Zotac Amp Extreme Edition)
32 GB Ram (ddr5 @ 3600MHz)