And the reason for reccomending a rebalance after joint replacement on GM's is most GM shafts used a glued in u-joint. They installed the joint until perfectly centered, then filled a cavity with nylon to hold them in. When you replace them youhave to burn thenylon out, and since they weren't meant to be centered off circlips agai,st the yoke, many times you can never get them perfectly centered, and never stop the vibration without a rebalance. Most 2500 and up use a circlip to center the joint, so its not a real issue with them.