Thanks, Marty. I took the camera downtown yesterday with a 28-300 on it and did some fairly extensive shooting. Most of the time the camera would autofocus properly, but every now and then it would hang. Of course the hang always comes at the worst possible moment. Later in the evening I picked up the camera again and found that with the 28-300 on it, autofocus has failed completely. I tried some of my other zooms on it and all of them gave me mixed results -- autofocusing sometimes and failing other times. Finally I tried the 28-300 on my D800 and found that its autofocus was dead on that camera too. Now I'm afraid to try my other lenses on the D3 for fear the body will clobber them too.
I explained all this to Nikon this morning. I'm sure I'm going to be sending the body and the 28-300 in for repair. At least this time both the body and lens are under warranty.
Worst thing is that I have a shoot scheduled early next month for the dress rehearsal of a play. I did the last one with the D800, and the post-processing work just about did me in. I want to do that shoot with the D3. My fingers and toes are crossed.
Edit: Camera and lens are on their way back to Nikon. We'll see what happens next.