Tow,
Aside from the 8 bolts from the center section, there are 8 tabs(2 on each side and 4 across the bottom) that are holding the grille in place. If you look closely around the grille you can kind of see where they are. I was able to change mine out without removing the bumper cover because I already had the Denali grille that I purchased from one of the other members and I could look at that grille and see exactly where the tabs were and in what direction I needed to apply pressure to pop them out. After I got the first one, I was able to pop out the other 7 within 5 minutes. Removing the 2 screws holding in the front fascia right next to the headlights helped to give me a little more arm room.
Obviously mikefdny's suggestion is the right way to do it. Just letting you know, that's how I did it.