Jim&Carolyn,
Congratulations on your new AF811 and GMC 3500. I bet you're getting anxious for the big day to arrive! Please post pics when you get it loaded up.
We're running an 855S on a F350, with no additional mods at this time. The truck handles the load amazingly. It is extremely stable, doesn't flinch when passing, or being passed by, large truck or buses. However, we will likely add some sort of suspension enhancement in the future to reduce the squat. I haven't been too inspired since it handles so well, but would like to get the headlights in a better position when loaded.
Anyway, I would agree to postpone any changes to your new truck until you get some miles with the camper loaded.