Low FPS in Game

For the past month, I've noticed my FPS has dropped, fluctuating between 60 and 80. My GPU never reached 100% usage, and I thought it was a processor issue, but today I tried setting Nvidia's multi-frame generation to x2, and my FPS jumped to my target of 157. Do you know why, even with the preset on low, I never reach 157 FPS, despite my GPU being more than capable? The images show the three scenarios I mentioned earlier.