The 380 is probably very close to last generation the 280 family; improvement may not be much.
But what you can try is see if there are any GPU throttling. This happens when the GPU becomes too hot or try to stay under the rated wattage.
First, let's try opening CCC and Overdrive. We are going to up the "Power limit settings" to its maximum. Run your game again, and see if there is still a lower FPS.
Let us know if that helped!