1995 Ford Escort Front end vibration

1995 Ford Escort Wagon with an occasional front end vibration. Car very rarely exceeds 45-50. But occasionally travels 20 miles at 60-65. The shake comes in at 60-65. It may start after 5-6 miles, it might start immediately, requiring a slow down. It may do it under load or in a turn or it might not. Car has 110K. The mechanics say tires are balanced, ball joints and tie-rod ends are tight and struts are fairly new. Any ideas where to go next?

The next best bet would be the tires, does it have rear struts? Is it possible to isolate it to front or rear?