highway vibration

I was going to suggest the steering box mounts cracking. Mine did that and it was like the front wheels of a grocery cart at 30 mph !CRAZY speed wobbles, like slam on the brakes before your car shakes itself to pieces bad. Good you found it, the Explorer 8.8 uses the axles riding on roller bearings too, strange design if you ask me. Bad bearing, replace the axle! lame.....