I'm looking for lowering kit for 04 silverado reg cab 2/4 it has 6.0l supercharged the previous owner cut the front spring and take one of rear leaf I can't control it ,which is the best lowering kit , and for control do I need to change sway bar or install truetrac diff help me

 

This my truck

 

First off I would start by buying new springs and rear leaf's form the junk yard. Than decide on what brand lower kit you would like to have, and how low you would like to go!!
I would definitely recommend you to get some Cal-tracs, and some better shocks. I would also get some 20" Drag radial's. I think this was my friends truck before. Does it have a Carbon Fiber Dash?