I think this is likely what it is. I have experienced what you're experienced, choppiness at 60 FPS with Vsync OFF. Usually its just that the game engine has big frame time spikes. Sometimes its because without vsync you lose the frame smoothing lock-in that Vsync can cause in some game engines. I always play Vsync ON because of the increased smoothness and the fact I cant tolerate tearing at allIf you showed a video, we might better answer the question. At the moment, we can only guess.
Back pressure is a reason V-sync can be good. With V-sync on, the GPU is held back a bit, evening out the frame times. This results in a smoother delivery. This may vary from game to game as to how bad it is.