SOLVED: All Windows versions seem to have the same behavior. I tried another version on another partition and it had the the same behavior, so is not the O.S, its something else, could be the nvidia driver behavior. Anyway, thank you everyone for the suggestions, this thread can be closed now. So I have been at Windows 10 1803 for a while, don't really know why, it just seemed like a good version to me, but in reality it had quite some problems, even with a clean install. Anyway, I decided to clean install Windows 10 1809. But now I have some odd issues related to Borderless Fullscreen. First of all, a baseline: I reinstalled the nvidia driver and used DDU to be sure there are no problems, but still the issue persists. So here is the problem: Games at Borderless Fullscreen have worst framepacing or frametime than they had at 1803 on 1809. (I also tried updating the system to 1903, but the issue remained, so I just rolledback). I like to use Borderless full screen at some games because I feel they work better that way, not all of course, but some I prefer to play them this way. I always measure frametimes with RivaTuner, on Widows 1803 at R6S (or any other game) the frametimes were perfect at email@example.com ms or 60 fps at 16.6 ms at Borderless, rock solid, never moving, without me needing to use any framerate limiter. On Windows 1809, this isn't the case anymore and the frametimes are just worse on Borderless, fluctuating from 13.1 ms to 13.5 ms (75 fps) or 16.5 ms to 16.8 ms (60 fps, v-sync on), I have no idea why. I have ran sfc /scannow twice and it reports no corrupt Windows files, somehow seems DWM is damage. As I said, this happens with any game at Borderless now under 1809. I know I can play on Fullscreen or just use RTSS to limit the framerate to get good frametimes; but the thing is that I didn't need to do that before, so it means something is messed up and as I said earlier, I need Borderless for some games, I like them that way. Others do work better at Fullscreen. Is it just me or an "quirk" from newer Windows version? Could anyone else try to reproduce this problem I am having by testing any game? Please help!