After reading your questions and the replies I just had to throw in my two cents. I'm running the 4.5 inch Rubicon Express springs and they are not bouncy. But I had a pair of Black Diamond springs once and they rode really rough. There are several tricks you can do to make the leaf springs ride well.
Step one. Use factory rubber bushings in the main eye of the spring. They flex better and hold up well. Try to stay away from the poly ones because they are just too stiff.
Step two. Only torque the main eye on the frame to around 80 pounds and use a locking type nut. You want a snug fit and not super tight. The shackles should not be any tighter then 30 to 40 pounds. Again with a locking type nut.
Step three. If your spings have spring type retainer straps then have then opened up to allow the spring to flex more freely. Most custom off springs have an open type retainer with a bolt.
Step four. Remove the springs and pull the pack apart. Clean all surfaces and repaint with a graphite paint. Also if your springs do not have teflon pads then that is a good time to have the leafs drilled and pads inserted.
Step five. Remove both track bars and throw them away.
I know this is a lot of work but the cost is low. Just a lot of sweat. My YJ rides great and flexs well.
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Have fun and don't bang your knuckles too bad.
AJL