I am also having an irradic frame issue since the update to 10.5. My frame rates keep dropping to 19.90 (always that number). I had tried the obvious things like adjusting my settings, etc. There doesn't seem to be an correlation even after restarting x-plane and restarting my computer. At first I thought that the 10.50 upgrade must have been much more performance hungry. I adjusted my settings. Sometimes they would work fine at a higher rate, others not. I thought I had it fixed by lowering my settings, but now it has dropped down to the good old 19.90 again in the middle of my flight (and this is after it was running in the low 40s frames / sec). Can someone please help with this ? I don't see how it has to do with windows (and I have all the latest updates). I have a Asus GTX 770 video card. Also, I was not using Alt + Tab.Thanks