If you have an 8.4A, it's already in the radio and you can have the navigation "unlocked".
8.4AN radios from the factory have the navigation already enabled and can be set to "pop up" on the dash 7" EVIC. When you unlock 8.4A navigation, it does not have this option. Maybe someone who has swapped in an 8.4AN radio can verify if this feature is possible to be added.
Before spending a bunch of money, read up on what others say about the factory navigation. It was already in my truck when I bought it, knowing "how well it works" I wouldn't spend the money on adding it to my truck.