Here's why: Your truck will sag just as much when heavily loaded, and will ride much harsher during the 99% of the time it spends unloaded. Shocks have NOTHING to do with sagging or ride height, that is strictly dictated by the springs.
The constant added mass of a bumper/winch combination needs both stiffer torsion bars to withstand the load without wearing out prematurely, and stiffer shocks to help dampen the added inertia of the heavier front end.
That said, I have 20% all around with only a fairly light TJM T17 bumper up front. I don't mind the stiffer ride, and I do like the improvement in overall vehicle stability they provide. When I have had my X heavily loaded on the trail (I sleep in my X so I carry all my gear around with me), it controls chassis motion quite well and others riding with me have remarked how smooth it was at speed on uneven gravel roads and such.
Brent
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