One thing you should have found with your searches:
"It's always the accumulators!" 
Rarely if ever is a harsh ride anything but the spheres, ie: accumulators. Also if they are compromised the leveling valve doesn't work exactly as it should.
You may still have sagging issues after you turn the wagon off and it sits for awhile if the valve is leaking internally, but when running it should be right as rain......
Also, be ready for the high pressure line to blow after you replace your accumulators. Both of my wagons did that not too long after replacing the accumulators.
If I ever get another wagon and have to replace the accumulators, and the high pressure line under the hood is original, I will have it rebuilt at the same time. {$60 bucks at hydraulic hose shop}