Over the last few weeks, I've noticed that between shots (intermittently) during a lengthy shoot (action/sports), my D3 will shut off. I'll raise the camera to eye level and try to focus by pressing the shutter 1/2 way, and, NOTHING HAPPENS even as I press the shutter all the way down. Also, the view finder will go completely dark and the rear panel LCD may or may not go dark. I'll immediately turn the "ON-OFF" switch to off and then back to on, and everything works fine. A few or several exposures later, the problem repeats itself, and each time I reboot. There is usually a few seconds to maybe two minutes between shots. The problem has been occurring more frequently in the last few days, almost on a regular basis.
On each shoot, the battery is fully charged as indicated by the bars on top panel. It's also been recently recalibrated. I called Nikon Service this week and they had me reset the camera. That seemed to work for a little while, then the problem resumed yesterday.