In your flights do you, at any point, have the EFB Flight Planner app opened? There seems to be a pretty serious bug that causes this kind of stuttering that gets progressively worse until the sim has to be shut down any time that app opens - and the issue continues even once it’s closed and the flight ends. Severe FPS drop and GPU underutilization when opening EFB Route Planner (introduced in SU3) - #4 by Zadma