GY-521 in particular and MPU6050 in general make quite poor IMUs. Why do you use them? And what for in this particular case?
What do they do in this set up?
Do you have other sensors in the same price range that you'd recommend instead for most uses? How much accuracy improvement would you expect?
Yaw drift is my problem, so I tried a bunch of IMUs.
Ones built around BNO055 seem to be alright and they are not that much more expensive.
I ended up using Adafruit's.