Air Bags.

I use the Firestone air bags with separate fill points, and an air bubble to add air. They work very well.

Air bags can be a great addition. They are designed to restore ride height and increase load capacity, but they will not increase GVWR. They do not help with sway control, as a matter of fact they can make sway much worse, especially if the right & left bags are plumbed together. If you need to reduce sway then you should look into a larger rear anti-sway bar or (depending upon your truck) upgrading your overload-spring bump stops (see: StableLoad)
Note that air bags can cause harsh ride quality, especially at higer pressures. This is due to their rapidly rising spring rate. This can be somewhat overcome with the addition of ping tanks.

I use Firestone RideRite airbags with an in-cab control system, and I am very happy with them! But if/when I replace mine I will be going with PacBrake bags (IMO, the 'best brand').

Cheers
-Mark

Firestone. Will never be w/o them unless I get a 550 or 5500 then we'll see. I've found sway is actually increased if I over fill. A rear sway bar may be cheaper and better if that's the primary concern.

X2 on the Firestone kit. Will never tow without them. I have had them for almost 10 yrs and what a diff they made. With a 5er it makes hooking & dropping a breeze and takes a lot of stress off the landing gear motor which will extend it's life. Bought mine from Summit Racing.

I use the Firestone ride-Rite kit with the in-cab controls. Works great but as mentioned, does not increase your towing capacity. It just helps with towing level.

I have the Airlift 5000. I plumbed them separate to lift the rear and balance side to side. They keep your headlights out of everyone's eyes.

As already noted, they do not help with sway and will cause worse sway if you lift the truck off the overload springs.

I air mine then let them back down just enough to engage the overloads.

They do the job of raising and balancing the rear end well.

Last weekend I used them to raise the truck about 6 extra inches so I had a bit more room to work under it.

I've had airlift and firestone on two different trucks, both rated 5k lbs and double bellows. The airlifts were on a 97 and it was a drill kit... I drilled the holes where I wanted them. My 03 is the no drill kit and they replace the rubber stops. Both work great. I use them to keep the back end up and help the ride when towing. I joined them with one airline to keep airing simple. I don't know if separate airlines would be any better for sway than the seperate springs that you already have. I think the best thing for sway would be a sway bar. Craig

They do not help with sway and do not increase your tow/weight ratings.