I have noticed during flight that even when I am getting a consistent 40-50 fps, I look at the ground as I am flying over it and there are little jitters in the rate of motion over the ground I can best describe it using text as: normal,normal,normal,bit slow,normal,bit slow,normal,normal....(no pattern to repetition) this might have been what I saw in say a 3 second period with the slow jitters lasting not even a second but definitely noticeable during which my fps stays between 40-50. As far as my experimentation, I changed flight model from default the 2 to 3 and even tried 1, no difference. Edit: Some more diagnostic information: Happens both in X-Plane 10.35 32 and 64 bit. (It was happening even before the 10.35 upgrade) Happens on a range of aircraft I tried from different manufacturers both payware and freeware. Helis and fixed wing. Even happens with default aircraft. In all instances my frame rate was above 40 fps, sometimes even above 50 fps I tried absolute minimal rendering settings and got consistent frame rates of 50+ and it still happens. I don't use HD mesh. Other research indicates that X-Plane 9.70 does not have this problem on my machine.