Lowering your suspension will drop the trucks' centre of gravity which improves road holding during turns. It also has a small impact on wind resistance but you won't notice any real improvement without other mods like a front air dam (this will help reduce 'hovercrafting' at freeway speeds). Drop the ride height by not less than 2 1/2", get your hands on bigger diameter wheels with lower profile tires, match your shocks to accommodate the ride height drop (if not, at least buy new shocks all round) and your truck should feel a lot more user friendly.