I had a somewhat similar issue, and wondering if my fix might help you?
TLDR; Turning HAGS off and restarting my system seems to have fixed it, but now there’s no NVIDIA frame gen.
My issue was a “rhythmic” stutter, roughly every 3 seconds. Nothing apparent on RTSS frame time graph, but my 1% lows were in the teens. Otherwise I was running at a stable high 140+ fps.
This is on a 9800X3D/5090/64GB desktop that previously ran the game without hiccup.
After extensive troubleshooting, it appears that something in a recent update messed with the scheduling on some systems.
Noticed that many others were describing stutters since one of the winter updates.