Two years ago, the shaft of the pinion gear broke shortly after shifting into 3rd gear at about the 1000' mark. As part of the repair exercise, I replaced the ring and pinion gear set, axle bearings, rear U-joint and balanced the drive shaft. This past weekend I noticed that I have a high speed vibration. I don't notice it in first or second gear, but starting about 4600-4800 rpm in third gear it starts. It is a pulsing, rhythmic vibration that doesn't seem to emminate from anywhere in particular. It does not feel like it is from an unbalanced tire. Any suggestions? Thanks.