Driving on the highway the truck starts to shake at 65 to 70 miles per hour. I had the 2 front tires re-balanced. I checked the air pressure in all four tires and checked the rims. Shocks are new. What else should I check:shrug
This might not do you much good, but the 91-94 Explorers had the same problem, something about the natural frequencies of the metals and the parts, not real sure what caused it, but Ford put out some sort of "fix" under a TSB for it but again, I can't remember what it consisted of.
When I first put a lift on this truck, the bolts loosened, and the rearend shifted. That caused some bad shakes. But there could be several causes. Check your drive shafts, u-joints, and ball joints. You did the front tires, but did you do the rear? You could also have a bent rim or axle. And there could be a broken leaf. That should give you plenty of things to check for now.
What kind of shakes have you got? Did you check ball joints, wheel bearings, etc? A quick shake of the front tires can tell a lot. If you end up with the rear shaft off, try lubing the slip joint and tightening the pinion nut on the rear. This took care of my shakes.
I found out my 2 back rims were bent and I could pinpoint exactly at what point in time my truck started to shake back and forth so hard I thought it was gonna roll at 70. Shortly there after I happened to get new rims and 36" Bias plys and have only gone 80 so far but its much smoother.