What sort of trailer hitch are you using? A simple ball on the bumper won't be enough- - - -you need to install a Class III or better square tube receiver hitch and use a Reese, Valley Tow-Rite, or some other brand of load-equalizing hitch that transfers some of the tongue weight to the front wheels. Simply "improving" the rear suspension capacity is just hiding the problem, not solving it. BTW, your air shocks should only be used to level the vehicle from whatever load is in the bed BEFORE hooking up to your trailer, NEVER to compensate for squat after hookup.
I started towing travel trailers in the mid-1960's, and I was building load-equalizing hitch receivers from angle iron and flat stock long before bolt-on Class III hitch receivers were invented.
Jerry
