Truck and trailer near max load, still need more gear...

This is what many RVers do.
Check the specs difference between a 2500 and 3500 for your year, make and model.
If it is just suspension and axle, motor and trans are the same, then beef up the suspension.
Many people use Timbrens or air bags or helper springs or new springs.
Also check the load rating of your tires.

A WD hitch puts some weight on the front tires also, so you will need to weigh your rig axle by axle after you are loaded for a trip to see where you really need help.