Thanks Jerry! I had my son drive the truck down the road while I laid in the bed with my ear to the floor. Not as much noise as I would have expected. I did take off the driveshaft and the differential yoke (wow that nut was on there!) there is no "in and out" slop of the pinion but the pinion seal was shot in fact it was hard to keep oil in the rear end. Anyway I am thinking its gear backlash in the transmission but if you are ever in the area, I will have you give it a drive and tell me what you think. There's a free lunch in it for you :-)
Joe
