Since you are towing a 5th wheel you have several choices. Roadmaster AS, Timbrens or Sumo, or airbags.
Timbrens/Sumo are only active when there is weight in the bed and wont affect ride quality when empty, which is a plus in most cases
Roadmaster Active Suspension is all time active and can improve ride and handling, especially with worn springs. I have these on my F350 and made a huge difference towing and empty.
Then there are airbags. Probably the most expensive solution, and the only one you have to muck around with when hitching and empty where all the others are set and forget.