I tand to agree that it might be a tire issue, too. A damper won't fix a vibration. It's been stated that the steering is tight, new kingpins, etc. That leaves something in the rotating assembly. Could be an out of round tire, those can be balanced, but still give a vibration. Same for a bent rim. Here's one more thing to add to the mix-Are the lug nuts light? Lig nuts should be torqued, just like head bolts. The spec for the old 6 lug 1/2 tons with the 7/16" studs is 45-60 ft/lbs. Too much can warp the hub, not enough can make the wheel wobble on the studs, and even come off the truck. If they've been run on with an impact, especially if they were just hammered down like most shops do, the studs may be stretched and never hold proper torque.
