my truck is running a main spring, and overload spring, and 3 inch lowering blocks. if i were u i would just start with the blocks.
installing blocks...
1. jack up truck under frame and set on jack stands
2.put jack under rear diff untill its supported by the jack
3.remove nuts from U-bolts
4.remove u bolts
5.jack up rear axle 3 inches
6. insert a block in between leaf springs and axle on both sides
note:blocks will have a hole in the bottom and a nub on the top there is a bolt on top of leafs that gos in hole and a hole in bottom of axle to insert the nub on top of block.(self explanatory)
7. make sure you are lined up good
8.replace old u bolts with new ones that are 3 inches longer to incorporate blocks(MAKE SURE YOU BUY A KIT THAT COMES WITH BLOCKS AND NEW U BOLTS) this kit is only 20 bucks at schucks/kragens
9. tighten everything very snug to make for a nicer ride and to eliminate any unwanted sounds.
10.good luck should take about 30 minutes