Act overlay causing stuttering.
I've narrowed it down to the overlay, turning off the overlay will make them go away. Using windowed (not borderless) will work. Forcing that windowed mode to borderless (via borderless gaming) will cause it to stutter.
I had it working before but had a few recent changes. Upgraded my monitor to a Samsung QN90B and upgraded windows to 11. I doubt it's the monitor, but I've read in some posts that Act doesn't like 144hz (old monitor was 120). Other than that it might just be windows 11? Without act all of my games have been running better on 11 than they did on 10, so I don't think I will revert back. Hopefully I can fix this so I don't have to play in windowed mode if I want to have act running in a raid.