How much distance do you have between the upper secondaries (overloads) with no load in the bed? Springs have a 'rate' and leaf springs especially have a graduated rate as you compress them and they resist more. If you have at least 3" of space between the springs and the upper stops, S.L.'s will help. Adding another upper overload springs will also help if you are carrying a heavy load, i.e.: at least a 4000 pound payload, which yours will surely surpass. Short of completely replacing your springs with a higher spring rate set, S.L.'s, or a facimile will be the best bang for your buck.
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