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.