I have a set of airbags on the rear from the previous owner, I have no idea the make or model, but do they increase towing capacity? If so, how much?

 

I'm sure the back won't sag as much with the bags, but keep in mind that the tow rating covers your vehicle's brakes and the amount of weight that's able to to controlled/stopped.

 

It does not increase your tow rating. It helps with heavy trailer load control though.....

 

no airbags do not increase towing capacity, just stops the rear from sagging under the load as much, on these trucks the limiting factor seems to be the braking system however im sure trying to control 7200 lbs with a D would be quite a time . . . (difficult i mean)