1994 Ford F-150 bad vibrations

1994 ford f150 4x4 5 speed manual transmission

the truck started to vibrate about a month ago I was driveing at highway speed it started to vibrate it when I was on the concrete portion of the highway it would stop vibrateing once I was on asphalt portions of the highway but now the truck vbrates all the time at speeds above 50MPHit feels as if the tires are out of balance
this what I have done: had the tires balanced, vibrations continue after it was balanced had the tires rotated and rebalanced the tire techs check for cupping or any other tire probleams and they found none had an alignment done. Made sure that it was out of 4wheel replaced tires it still continue to vibrate ***NEW*** I jacked the truck of the ground strated the truck in two wheel drive checked the drive shaft, I put the truck into 4 wheel with speed of 20MPH, but the rear driver side wheel spun slower then the other three. Was able to stop and hold the tire with my bare hands and was able to spin the rear wheel, the opposite direction as the others where rotateing. Found.030 of inch of in and out of play
on the rear wheels.