We have a 2006 GMC 2500HD Extended Cab 4x4 6.5' bed. We have an Outfitter Apex 8 camper.
I am not sure if the rear spring package is the same as yours. Ours has the overload spring under the spring pack. The significance is that when our camper is on, we want the overloads just touching the bottom of the rear spring package.
Our camper weights 3200# to 3500# depending on the trip. We have air bags to help carry the load but have found for reduced sway its best to fill the air bags to just before the rear spring pack is off of the overload spring. Its worked well for us.
We also have KYB Monomax shocks which we are very satisfied with.
Bubtoofat makes a good point on tires. We have Michelin LT285/70R17 D rating 3195# each. The tires are filled to 65 psi with the camper on. The fonts do not get any more air because my truck only carries about 300# more on the front with the camper on.
Sway is not an issue for us.
Good luck.