This theory is completely wrong... why would the GUI Trackir in OpenGL should affect the output data for the DCS?
Graphical Gui does not run in overlay, to influence each other. Such a mistake was quickly revealed in the beginning of the development of the TrackIR.
You have a completely different problem, your hardware is too weak to be able to tighten the constant 144 fps/Hz gaming monitor.
If you suddenly fall images from the values 144fps on 65 so it is clear that the image can never be smooth.
Set the details so that you have at all times had the most constant framerate and trust that TrackIR will work great with G-Sync and FreeSync, anything else it is not.