My dealer was happy to give me a new D600, so I took it and tested it with my same lenses. The second D600 was worse!! My lenses were up to -11 and -16. I wondered if my next lens might be off the charts.
Bottom line, I returned it for my original D600 and will stay put! I assumed a new Nikon would be more tightly QC'd with autofocus.
None the less, I'm still very pleased.
Thanks for all the advice. No need to try a third.