What I have seen is that when the mouse and keyboard is idle the GPU can drop its clock rate which has the inverse effect on the GPU % Load reading. While that is expected I can't tell you this is an issue yet.
Then we get to reveal that all these measurement apps could be in error about % TDP as they calculate off the GPU load.
The 750 has been out for years. I don't expect this to be a new problem for you or others but suggest you use the drivers you used for years that worked. The most common encounter with issues like this is when the owner installed a driver updater app or read an article that told them to update all drivers. Again, this is the usual cause. My view and many others is to never change drivers when it all works.
PS. I did no further research on this. You should find this issue with a google.
In any application, I'm experiencing frame drop of sub-10 fps after i idle my mouse and keyboard for about a minute. Once i move my mouse at all or I type anything on the keyboard it returns back to normal. This is really frustrating when watching any type of video. Also, I discovered that my GPU usage shoots up to 100% during this low fps period. I've already explored the power options in windows and the performance settings in nvidia control panel, making sure everything is on the highest performance level. I will include specs and a screenshot of GPU-Z below. Any help is appreciated.
AMD X4 860K
2x 60GB SSD
Gigabyte F2A78M-HD2 Motherbard
Antec 750W PSU