I have a 93 GMC 3500 van I use for work. I just got it recently and don't know much about it's history. My rear drum brakes have issues. They pulse rear bad, sometimes to the point one wheel will lock up. Usually it is the worst at speeds of less than 15mph. Sometimes they are fine though. I don't know much about drum brakes but I have been playing with the adjusters and have not made much headway. I replace one drum because I thought it was warped (it was the one that was doing most of the locking up). Now the other side is worse. I noticed the other day while laying under the van and spinning one of the rear wheels that the drum move up and down in relation to the backing plate. The rear axle is a semi float. Could the ends of both of the shafts be bent? I would imagine it it's a 14 bolt. I should check though.