Wow you sure got a lot of ideas here. Some completely contradict the other but that's what opinions are all about.
I can only speak about my Dodge 3500 dually so it may be a different result for your GM truck. I added air bags and found that they lifted the truck off the overload springs and really made a side to side sloppy ride. I then added Torklift Stable Loads and it firmed up the ride without using the airbags much. I added Bilstein 5100 shocks to dampen the rocking (they don't provide any height lift). I use the airbags to simply level the camper.
I think the advice you have received about springs is right. Add airbags only after trying the springs if you need to level your loaded truck. Good luck with your suspension mods.