Uhmm it might sound crazy... But it happends to me when playing shadowverse... Wich is a very light game, it dosent actually force any of my components so my 2 gtx 1080 goes iddle when playing Shadowverse and in the game i only get 30 fps as maximum instead of 60 (cause the game is automatically synched) so i open any other game to run in the background to force my GPU to work. Maybe you can try to open a minor application to see if you can force the GPU to work at 100%
Didn't work sadly. I lowered the settings in FO4 to high with no improvement to frames and the usage dropped to 30-40. Something is telling my GPU (probably the driver) that it's doing enough. Idk what it could be as it's a pretty new computer (less than a month old). I'm going to try to uninstall some of the un-needed MSI utilities as they have caused me a lot of complications so far, maybe the problem lies somewhere in there.
UPDATE: Welp uninstalling some of the MSI utilities did actually help a bit but didn't solve the problem entirely. Im up from 26- 50 frames in downtown to 40+. I'm not quite ready to say solved as GPU usage is still sitting at a now steadier ~45 and frames could improve but at least its playable now.