Sumo Springs (and Timbrens) are both good choices for what they are intended to do, but certainly do NOT perform the same function as shock absorbers!
I have been happy with the shocks I installed almost two years ago along with new rubber shear springs for the LRE 4000 equalizers (factory OEM).
Also installed new shackles and wet bolts as well as a MorRyde X-Factor cross brace between the equalizers.
These mods plus the new updated Sailuns make a pretty decent riding setup.
EDIT: I'm sure the MorRyde IS is better, but the cost/benefit doesn't work for me. The rear air assist suspension on my truck and the Reese Goosebox also contribute to the smooth towing...