If you start the SP3 with the mouse flattened do you still have lower res? I have full 1920 x1080..
Yes. The mouse was flattened (paired, but not connected) when I unboxed and setup the MWDA and I experienced the lower resolution. In fact, the Arc Mouse was in a drawer in the next room. It wasn't until I read somewhere online about a possible compatibility issue that I even thought to look for the mouse. I had to disconnect it the Bluetooth Settings screen on the Surface before I could get 1920x1080.
Is you wireless connected via 5GHz or 2.4GHz (don't know what router you have). I'm connected over 5GHz here and I don't see the issue with the mouse flattened.