It was tight enough fitting a large exhaust under the truck with a stock ride height. With a 5" drop, the exhaust would be crushed between the bed and the axle. There simply isn't enough room. Because of the clearance, I had to make the decision to go to an exhaust stack and I REALLY don't like stacks. I could have gone and modified the exhaust to exit in front of the wheel, but I didn't like the idea of regularly wiping soot off my bed and wheel. Not that my truck smokes much, but just one less thing to worry about.
The DJM shackle is a 2" drop shackle which gives roughly 1" of drop at the axle. You can't really fit any longer of a shackle without hitting the bed. If you need a serious drop, then you'll need to install the front perch kit as well. Also, make sure to get shorter shocks or you'll have problems.
As for the springs, I removed the overload spring and the 3rd spring in the main pack. This gave me a little more direct drop and softened my ride considerably. I don't tow anything so I didn't need the extra capacity the extra leaf provided.
I hope this helps.