Only a Mk4 nav can show 3D.

Do you have a Mk4 nav?

You must enable the 3D setting in the service menu:
Select settings
Prress and hold left hand side of MENU
Wait
In Service Menu, scroll down to 2nd page
Enable 3D
Exit by pressing MENU again

Then turn it on in the display orientation (head up, north up, 3D)