Usually, with stuttering, it means X-Plane is trying to do too much and there is a lot of task swapping going on. You really don't have too much going on from what I can see, but maybe try the "remove plugins except Gizmo" routine and see if that fixes it. If it does, it means one or more of your plugins is working in the background. If not, we'll have to look at what else is going on. So far, you are the only person who has reported this, so it's likely this is something on your end.