Check your settings. If you are using hairworks or a similar post processing affect, or a DSR to bump resolution to 4k for rendering and back to 1080p for display, it's going to put a massive dent in gpu power and drive usage pretty much to maximum. Great quality picture with all the shadows and gimmicks it can possibly get, but lousy fps.
The cpu pre-renders all the frames, so it sets a hard limit for fps. The gpu either lives upto that limit or fails, depending on the detail levels, post processing and resolution.
So if the cpu can kick out 100fps, but the gpu at ultra only puts out 50fps, lowering settings can raise that up. But can't exceed the 100fps cap. That's gpu limited and most common.
If the cpu can kick out 100fps and the gpu can put 100fps on screen at ultra, lowering settings does nothing, you are already at peak fps. That's cpu limited and most common for older pc's with underpowered/low core cpus and powerful gpus.
So figuring out if you are cpu limited or gpu limited can point you in which direction you need to concentrate efforts. Seeing 10% usage cpu and 99% gpu, either could be at fault, or both.