You need to make sure the following technical service bulletin was/is performed on your vehicle first.

"SU002-98 JUN 98 Suspension - Improved Ride Comfort for Rear Seat"

I currently have a 2001 4Runner but my previous 97 4runner LTD had a poor ride due to a problem with the rear springs/bump stops. I even replaced all the shocks hoping that would fix the problem. Then I found out about the tsb above that is the real fix.

Problem is now that your vehicle is this old you will have to pay for it yourself. I believe the problem was corrected mid model year '98.

My 2001 rides unbelievably better. Most friends could not believe I bought another 4Runner as much as I complained about the ride but the '01 was much better. I ended up trading my '97 in for the '01 and didnt get the tsb done....