I also have issues with this on my 2015 STI. The car pulls to the right when in the left lane on the highway. It also shakes when the car is really cold and I just put the DWS tires on. I have had subaru look into it a little and they said nothing is wrong with the tires. I do notice that after driving for some time the car is very smooth although it still pulls to the right.
I am going to have a mechanic friend of mine look into it.