Air bags are a suspension supplement not an actual suspension. Nothing you do to your truck will change it's rated towing capacity that is stated on the tag affixed to the doors B-post. That rating is also based on you running the correct tires at the correct pressures. I do use air bags, but my intention is not to carry more weight then legally allowed, but rather use them to allow a more comfortable ride. I removed the overload spring packs, and use the bags to support the truck, making the rear ride on air. It really does make for a much better ride, empty or loaded. My air bags are good for some 5,000lbs, but that does not make my truck legal to haul more then it's specified weight rating.
Towing at the maximum rating, requires driving on the defensive all the time. You need to allow room all around you in case someone does something careless or worse. People love to cut in front of others, most time without thinking about the guy they just cut off, his load or his increased braking time. You need to constantly think for them, what they may do, what you will do, it is a never ending chess game were you are constantly watching others moves and adjusting to them. My wife is the best co-pilot I have ever had, she fully understands whats at stake and how to adjust to the moves of others. She will not drive our truck, loaded or empty but she is more then capable to pilot it. It might sound goofy, but driving while towing a heavy load is exhausting, you are constantly on the look-out, adjusting and anticipating others moves. There is no room for hot heads, tailgaters or idiots while towing, sure others will make moves that are foolish, un thoughtful or plain stupid, but that is to be expected. Most people do not no what it is to drive while towing a heavy load, they do not think about the increased stopping distance, the inability to make sudden corrections or moves, or the extra amount of space you and your rig require. You are forced to think for them, out smarting them by taking a defensive stance and making the needed corrections before they come into play. Truck drivers have to be some of the coolest cats on the road, they deal with these situations every day. Just watch the way people cut them off repeatedly in heavy traffic conditions, many times at done with very little warning or with very little room. They have to allow for this and stay calm, how they do it day after day is amazing to me, I have seen many people cut in front of them and slam on the brakes thinking nothing of the semi driver or his load. When I see a truck that has that 1 million accident free miles written on it, I always give him the thumbs up, while what an accomplishment.