One reason why our vehicles ride so nicely when they are new is because the leaf springs are all slippery. So they slide over each other as they flex.
As the slippery surface wears away the ride gets worst and worst. There are ways to combat this.
The easy method involves simple hand tools, and a can of spray lube. WD40 won't work for this, it must be some sort of spray grease.
position the jack under the frame, and crack loose the lug nuts. Jack up that side and support it. remove wheel.
Now wedge a flat head screw driver between 2 of the leafs
spray some lube in there.
remove the screw driver and do the same to the other leafs.
On the front 1/2 you'll see a clamp like this
remove it, and do the same thing. Then clean up the threads and put it back.
Put the wheel back on and lower the jack. Don't forget to torque the wheel to spec's.
Do the same thing to the other side.
It makes such a big difference that I'd like to take the extra time to do this job every time that I rotate the tires.
If your on the market for new springs you can replace them with a set that has these grease able inserts installed.
I'm looking for a do it yourself insert set, but haven't found any that I like yet.