Your rear spring pack has probably sagged over the years and now you are riding more on your high load leafs than you used to be. The spring rate on the high load leafs is much higher than the first leafs. Thus your truck rides rougher.
The other thing that happens is rust builds up between the leafs and they stick instead of sliding nicely over each other. Although the overall spring rate of your pack may not have changed, the rate for small incremental movements, ie pavement joints, small bumps, etc. is very high. Google "leaf spring coulomb forces" for more info. Shocks may help some but the real problem is the spring rate of the leaf springs.
I had the same problem. I'm sick of riding around in a rough truck. I'm installing a full on air suspension on my truck. Its in the shop right now. I'll report back when I am done if there is interest.
Last edited by Me2000; 10-28-2009 at 10:05 PM.