You aren't supposed to be at 100% usage. It's a common misconception.
Usage isn't how much of the gpu is used, it's how much the gpu has to use. There's a difference.
When you lift a glass of water, you will use 100% of your available muscles in your arm, every tendon and ligament in your wrist and fingers. But thats entirely different from using 100% of the Muscle in your arm. You don't squeeze the glass as tight as you can, you don't struggle to lift it with all your strength, you don't 'wing' it up as fast as possible.
You just apply as much as is needed to lift the glass, but will use everything to do do. That's usage.
Your gpu/cpu is doing the same thing, using 100% of the resources it's using, but doesn't need to use 100% of All the resources.
Usage is a tool to use for comparisons and monitoring of the software the cpu/gpu is running, it's not a report of the cpu/gpu itself.
That said, what changed. What has been done to the pc/software that might change usage? Optimized game driver files added, windows updates, driver updates, changed monitors, dropped settings? What? Something has changed and since the numbers have gone down, that's actually a good thing.
100% usage means there's nothing left to give. If your dude is running through town at 100% usage, and a tank bursts through a wall that'll be a massive increase in physX, computations, vector analysis, particles etc, but the cpu/gpu has no more resources to deal with all that. No headroom. Making each frame take longer to populate, fps drops badly.
Having more headroom, lower usage means you have room for the additional effort required, fps doesn't drop as much.