Strong vibrations and noise

1995 Jeep Grand Cherokee, well maintained, 130,000 miles, near new tires. On road trip, going 65-70 mph, when hit bump or change in road surface, suddenly started shaking side to side, loud noise, had to slow to near hault to stop it. Happened about 6 times in 11 hr trip. Took it to mechanic (with good reputation). The only problem they could find was shocks–so we had those replaced on all 4 wheels. Another 8 hr. hwy trip–no problem. But on most recent trip, it did it again, twice. Vibrations not as bad as when it first happened, but same pattern–vibrations set off by going over a bump at fairly high speeds, and had to stop car to stop the vibrations. Help.

Have You Ever Replaced The Steering Damper (Fifth Shock Absorber) That Is Designed To Control Front-End Shimmy ?

You can check it by disconnecting one end and see if it operates with resistance and no bad spot(s) in its travel, but you might as well buy one and have it ready to install.