I have a '79 K-20 with the 465/205 combination. I have dealt with a slight vibration for 2 years. It developed and is not the result of a crash. I can jack the rear off the ground and the drivers side rear wheel hops up and down. I have gone from the 2 piece driveshaft to a 1 piece that was balanced and has new U joints. I installed a 2" lift a few years ago that has the blocks for the back. They are tapered to give a better driveline angle. I have dropped the tranny/transfer case so that the transfer case is pointing straight at the rear pinion. I have tried new tires and rims and there was no change. The wheel hop is only on the drivers side. Could a bent axle tube cause a speed specific virbration? Sorry for the long post but I am close to the end of my rope. Any help, opinion or advice will be greatly appreciated. I know this is not a K5 but this seems to be the forum with the greatest number of people who actually know what they are talking about.