360 Balance Question

If you have some way to get the vehicle on a hoist so the rear suspension hangs down, leave trans in neutral and rotate the rear tire/tires and watch the drive shaft as you turn them, you may have a bent or dented driveshaft and this would be the cheap free way to check it. Also look at the driveshaft close to the ends and see if there are any spots that look like a weight may have been knocked off. I spent a LONG LONG time searching for the cause of a vibration I was having that turned out to be a driveshaft that had been improperly shortened and was out of balance. If the driveshaft has a visible bend/warp/warble to it, replace it. If it's a missing weight, get it rebalanced.