I had my camera for couple of weeks before I sent it to Melville NY for repair. They were trying to tell me that I shoudl mess with Fine tune AF
, but that didn't help a lot. All of my pictures were soft. I've sent it to Nikon, waited 2 weeks for my camera to return and after they made adjustments to AF
it takes pin sharp photos even with Sigma 150-500mm.
If your camera is still under warranty I would just login to the Nikon support page, create troublecall ticketm and send the camera to them.
Out of focus, softness, backfocus are the very common D7K problems. Nikon wont admit that they did something wrong, but read the D7K forum on flickr and you will see that every other post is about out of focus pictures.