on yours I would just remove the overloads and level it out, if ya tow all ya got to do is add an air bag helper out back, not all the 06's I have sold a kit to have vibrated, only a few, maybe one or two, at least you can adjust the pinion angle , and then later have it welded.
Psycho on yours that is the way the springs were designed, you need to use a bumpstop like amtrucker was talking, it dont stop bottoming on large bumps , but keeps it from slamming down.
there is no full remedy for lowering trucks or cars, with most and all the lower you go the more you will sacrifice.