I gave you a chart to read, It might be hard to read but you can go to Mark Williams web site and down load it. The trans and rear end need to be parallel, it does not matter if the rear end is up or down from the trans but they have to be parallel to each other. The reason you want the pinion down a couple degrees is under acceleration the pinion twist up and then they are parallel and this is in forward gear not reverse. If you are not drag racing it then you want it closer to parallel. I have never in my life seen a rear wheel jump off the ground unless some major force has been applied. Are you sure it's not the clutch chattering?
