I always had the problem on my Pickup camper trucks with needing shocks with more dampening to help with sway, but with camper off that same shock would be over hard and ride rough. I tried those adjustable ones but they had other problems (returned them)
now that I have a motorhome I don't have the option of removing the camper, but had same problem, the stock Mercedes shocks were designed for a van body and were too weak.
Than someone introduced me to
Agile Offroad. This guy builds shocks for off road racers, but also happens to own a Mercedes Motorhome, so he went to work on re-valving a fox 2.0 shock for his motorhome. Best money I ever spend on rear shocks. solved my problem. Maybe call him and see if he has a valving solution for your truck that would work loaded or unloaded?