The air suspension will not cause the float feeling you describe. most likely it is because of an improperly setup WD hitch. a lot of people describe the feeling you have and just go out and get a bigger truck and use the same poorly setup WD hitch that is now masked by the heavier truck. read up on how to properly adjust a WD hitch with the air suspension (I believe Ford even has a page or 2 in the owners manual on how to do this!), then be sure you have the proper tongue weight and properly sized WD bars, too heavy a bar can cause the same issue because it will remove too much weight from the rear axle. then take it out and see how much better it handles.