Joe, How long are the long bursts? The reason I ask is because Nikon limits the length of the bursts to 100 in cameras like the D300 because of the potential for overheating (the internals.) I am not sure though why you are having this problem since the camera is just back from Nikon. Have you tried a total reset?
Turn the camera off and remove the battery.
Turn the camera back on. Wait for twenty seconds and then turn the camera off. Or leave the camera on until the clock battery is fully discharged - possibly a long wait...
Replace the battery and turn the camera on. This should return the camera to its original factory settings.