Video demonstration: https://www.youtube.com/watch?v=Qs7jsDgXjHs
This happens with any game but GTA V shows it most obviously. When not occurring the game runs at a perfectly stable sixty frames per second, this issue occurs precisely every 60 seconds, and lasts for the same duration each time. The CPU clock speed suddenly divides itself by a third and the framerate halves. I'm running the latest build of Windows 10, with the latest NVIDIA GPU drivers. Any help would be appreciated. The specs of my machine can be seen in the video.