The springs on the rear a relatively new lowered springs, 13 years old. I am not sure if it is the springs but maybe the shocks. They are the same age. There is a particular place where I drive frequently and there is a small depression in the road and if I don't miss it it feels like they have hit rock bottom. The other issue I think is that a 20-gallon fuel tank is located where the spare once resided. I am leaning more toward the need for new shocks. I had a chart showing that a shock-mounted verticle would cushion better. The shocks are angled toward each other more than they should be, I believe. If someone could post a picture of the stock shock location it would be a big help. Forget the pictures I googled and found a bunch. Dumb me!
I wonder if that "rock bottom" sensation over that depression is your overload springs making contact. I'd remove the overload springs and see how it goes. Worn out shocks won't cause your problem. I had one come off the lower mount on one side one time and never felt any difference in the ride whatsoever. I still don't know long it had been just hanging there in mid air.