Sorry to hear of your troubles. It is ashamed if this issue is still occurring because otherwise it is a fantastic camera.
In preparation for sending my D800 to Melville, I have taken a series of test shots and have put a subset in my Nikonians gallery. I'm not suggesting that you need to go to that level of effort but I think these images provide a controlled and obvious demonstration of the problem and a method to produce it. On post #25 and #27 of this thread I give some info on the test.
All that said, if you feel the camera is off in some way, then by all means, return it. I wouldn't spend a lot of time trying to prove to yourself one way or the other.
Note in the gallery: PDAF = phase detect auto focus, normal focusing CDAF = contrast detect auto focus, live view