I have that combo and I suggest you get your shutter speed up as switching to/from Dx or FX mode is not the answer.
Go into the SHOOTING menu and select ISO sensitivity settings, turn On the Auto sensitivity control and then scroll down to minimum shutter speed and select AUTO. Right click on AUTO and a adjustment line will appear with slower to the left and faster to the right. Move the pointer to the right one notch. Try this some and see if your shutter speed is not high enough to suit you.