I have a 99 Dodge 2500 Cummins with 130000 miles on it. Within the last few months it has developed a shimmy/vibration at about 35-40 mph and 65-75 mph. It is not a death wobble or anything like that but it is VERY noticeable. I have had the tires balanced 3 times counting when they were installed last year and once at a different tire shop. The guy at the tire shop says it is something rotating: drive shaft/u-joint, tires, etc. I did find the lower u-joint at the diff. with slop between the cup and strap, not the pin and cup which I thought was strange. The experience I have had in the past with u-joints is that it is a sustained consistent vibration through the speed range but I am by no means an expert on the subject. I also have one lower and both upper ball joints with some slop in them. Any ideas???