I am almost out of ideas. I believe your system should be able to handle the game, but as a last resort i would try if additionally to reducing the graphics settings as before, changing the resolution to 640x480 improves anything.
If that's the case, it might be a performance issue.
Ideally you would check the CPU and GPU load while it stutters.
I am a Community Moderator, and I am here to keep the Forum a fun place for everyone.
My posts represent my personal opinion. I am a volunteer, not a TTG employee.