Front End Shake Puzzle

[davew833]

The front end of my '94 LS FRONT wheel drive has begun shaking intermittently at about 60 mph on the freeway- more on curves. It shakes hard for about a second and a half and then stops for half a second, then repeats. It's perfectly smooth up to 60 and smooths out again somewhat around 70. The other night I removed the front wheels and checked the ball joints (with a pry bar), checked the tie rod ends, struts, etc., and found no wear or play anywhere. Then I rotated the tires front to back to see if that would change anything. I got the same oscillation even after doing that. So, I took it to a nearby tire, brake & muffler shop this morning. They spent about 90 minutes trying to diagnose it and couldn't find anything deficient in the front suspension either. They did show me that my right front tire had a little wobble when spinning that indicated a tire with separating belts and/or a bent rim. Tonight I swapped that one out with a spare wheel & tire I had and it made no difference. Vibration seems to be worse under acceleration than coasting. I'm stumped-- any suggestions?