suspension ?
 

I'm looking at getting an 06 or 07 silverado. the first thing i want to do is lower it, and make it even. do i need two inch lowering springs all the way around AND new shackles? I'm confused if this is considered a 2/4 drop or what. how much will this cost me and can i (along with a few other friends) pull this off in a day? I have access to a hydraulic lift. thanks for the help.