This problem started for me 5 or 6 weeks ago. I have updated all of my drivers (space navigator, mouse, graphics card) but the issue remains. A few seconds after opening an assembly, moving that assembly around the screen (panning, rotating, zooming, etc) becomes painfully slow. However, if I click/highlight a face (any face, on any part, but not an edge, it has to be a face) then performance goes back up to normal. I am using a GTX 780 graphics card which I know is not technically supported, but I have used these GTX cards for years and never had an issue like this. Anyone have any suggestions on how to resolve this issue?