Contrary to popular belief, airbags WILL lift most anything. That is why Fire departments use them to lift things fir rescue. In the case of adding them to a existing suspension, the thing to remember is by the time you have lifted the load an inch or two, you have (nearly) completely unloaded the existing springs, and the airbags are supporting the entire load. Any movement at all and the original springs come back into play - the perceived "firm up" people attribute to the airbags.
Just slapping a set onto your existing suspension will not get you what you want.
