I had a set in a dual Rodeo I had a couple years ago that we used as a service vehicle for chasing rally cars. They where O.K but seem to sag after 12 months use. In the end I had extra leaves added to the rear springs and that semed to be the ultimate solution to the rear end sag. Mind you the ute had a service body and would tow a rally car on a car trailer it would of been at weight limit if not over! The best thing I have found is the Firestone airbags. Not cheap but they seem to be the best solution for vehicles that you want to sit level when the vehicle is empty or fully loaded.
Anthony