Never cut coils. Its a very very bad thing to do. You can get a 2/4 or 3/4 drop for relatively cheap. A 2" or 3" front drop can be done in a variety of ways. For a 2" drop the BEST WAY to go is either getting lower control arms or 2" drop spindles. For a 3" drop you can do the same thing, lower control arms, or 2" drop spindle with a 1" drop coil. To achieve a 4" drop in the rear since you already have a shackle all you need is hangers to drop it to 4". Or you can locate a factory shackle and buy a set of drop leaf springs. The two companies that I would recommend are:
-www.djmsuspension.com
-http://www.mcgaughys.com/homepage-award.html
http://www.gmfullsize.com/forum/
Also surf around the street section of the gm fullsize forum. There are plenty of threads about the different drops available. These guys know what they're talking about and will all recommend the same things I have to you.
I didn't mention Belltech, mainly b/c they have had problems with their front spindles on the new body styles ruining turning radius. It's supposedly been fixed but no one knows for sure.
I should mention that i drive a 99 Silverado with a djm 3/4 drop.