[Mauzen]

The high GPU usage isnt the cause, its a symptom of another problem. Higher usage means the GPU is using more time for calculating the graphics. Unless this is close to 100%, it could still go faster, but something else is slowing the whole process down, so the GPU doesnt even need to use its full power. So the GPU itself doesnt limit a thing and is not responsible for the FPS drops.

What graphics card do you have? And what about the rest of your hardware (cpu, OS, etc)