To start, I'd like to ask where you are getting your information so we are looking at the same thing and so that we know what to correct if it's on our site.
Now I'm going to start making assumptions...
Is this the "DJM shackle +DJM bracket" kit that you are looking at that only lowers 3inches?
http://djmsuspension.com/product/fk3098-3/
If so, that kit consists of two parts that perform completely different functions.
The "DJM Bracket" part of the kit is the lowering component, it's the part that actually does the axle flip and lowers the truck approximately 5 inches. The "DJM Shackle" part of the kit actually acts as a lifting shackle on our trucks and raises the rear end back up about 2" to the three inch drop mark when combined with the flip brackets.
If you want to drop your truck the full 5 inches you only need to get the DJM Axle flip brackets and get replacement stock OEM shackles. This is the kit you need for rear:
http://djmsuspension.com/product/fk3098-5/
EDIT: You will need drop shocks with the 5" lowering.
If you later decided that 5 drop was too low, the DJM "lifting" shackles are the same thing as a Chevy lowering shackle that is available at almost any auto parts store. I understand if that sounds confusing, its just due to differences in suspension design. Lowering shackle on a Chevy is a lift shackle on a Ranger.