The springs support the weight of the vehicle. The shocks control the oscillation of the springs. This means that the shocks aren't sagging under load, your springs are. You could potentially just be trying to tow too much weight or your springs are too soft. The shocks probably are harsh because they are garbage, not because they have firm valving. Firm valving usually only feels harsh when it's either too firm for the soft springs, or it's just a bad design. Cheap hydro shocks have this affect in my experience.