Card seems to be stuck in low-power mode until I reboot

Graphics card is a 980Ti, connected to a 27" acer g-sync monitor. This started maybe around a month ago. I usually keep my computer on most of the time and have sleep/hibernate disabled. I'll load up and play a game just fine, then go do other things then when I come back and load up a game, it seems stuck in some sort of low power mode.

Just the other day I was playing RIFT, went and watched TV for an hour, loaded RIFT back up and I was getting 11-17FPS when I usually get 60+. Tried quitting and going back into it but same issue. Rebooted, and performance was back to normal.

Sometimes I can try switching the video modes from Maximized-window to full screen and back and it will fix it but for some games only a reboot will get performance back to normal.

Does anyone know what I can change to fix this, or narrow down what's causing this?

Any driver errors showing in Windows?

You can try disabling GameDVR in the Xbox APP , this has helped a lot of people in the past with regards of clocks and FPS issues on both AMD and Nvidia camps, I suffered from that kind of troubles with my 980TI until updated to Win10 Anniversary, it was kinda sporadic but yes it happened, it was mostly triggered by long periods of gaming non-demanding games like league of legends or browser games where most of the time the card stay at idle clocks... for me, in my opinion was some kind of bug in the drivers but isn't happening anymore but the issue with the GameDVR option in the Xbox APP which is enabled by default in Win10 Anniversary caused me huge troubles with both my AMD GPUs

what araxie said and make sure you don't have other programs running in the background that use lower speeds. on my system if I leave IE11(yes I still use it) minimized to the taskbar my gpu locks at the lower speeds and ignores my OC settings. even utorrent will do this to me.

edit: this is why I never understand people that insist on multitasking while gaming. other shit running is going to take way game performance!

Thanks for the replies. No errors or warning appear in the event viewer when it does this. It's like the computer considers everything normal.