Not to be rude, but this post right here takes the case of the most ridiculous post I've ever seen on these tech support forum.

First off, why are you complaining about 1 fps fluctuation? Your eyes cannot tell the difference between 59 and 60.

Second off, why would you pair such a powerful graphics card with a 1080p monitor instead of a 4k? The 1080 is way way overkill for a 1080p monitor, and also, why in the world would you run your monitor at only 60hz when it was built for 120hz? Your gameplay will be smoother if you set to 120hz.
What you are describing here tells me that you are running at 60hz and have vertical sync enabled in the games graphic settings. v-sync will limit your graphics cards maximum frames per second to match your monitors refresh rate, which is set to 60, so you cannot go over 60. If you disable v-sync, then you will probably see FPS at or above 120. This is also why when you go into graphicaly intensive areas that, your FPS doesn't drop. With your 60 hz and v-sync enabled, you aren't remotely close to using your card to its fullest potential. It has nothing to do with the game or nvidia drivers.

However, with this said. I wouldn't recommend running the game without v-sync as this will likely cause graphical tears among other graphical glitches. If I were you, I'd go with the 120hz setting. This will also allow your game to run at 120fps instead of 60. If you want to verify what I'm saying, then go turn off v-sync. Your FPS will skyrocket. The same is true if you set your monitor to 120hz.

There is no game to date that I know of that the frame rate remained the same throughout the FPS always varies due to the complexity of whatever scene is rendering.