It was tires not balanced correctly on mine. A regular tire shop doing regular balancing can do a good job if they choose to. Many shops get within 1/4 oz and call it good. That may work okay or at least not that noticeable on the back but on the front it can go right through the front end parts to the steering wheel. Just happened to me. Rotated the wheels front to back and the steering stopped shaking. Took it back and had them re-balance the wheels I paid good money to have balanced right the first time. The road balancing thing is probably more precise but a good standard balance, IMHO, should be adequate for these rigs. They aren't Ferrari's or GT40's. Saw the movie over the weekend. Good stuff!

Also had a small bit of play in my rear u-joint which caused a kind of low roar. Driveshaft shop said I needed a new driveshaft too because it was .040 out of being straight. A PO had dropped it to flat tow the rig. Literally dropped it on the asphalt which apparently can be enough to put that ever-so-slight bend in it. I kept the driveshaft. If the one in my 98 goes bad I may just put it in it with new u-joints and see if I really did need to buy a new driveshaft or if I just needed new u-joints. I've had bad luck with shops in my smallish town. They talk the talk but they can't walk the walk or they are simply trying to con their customers. I think it's probably more of a con than anything else. I think they know better. I'm running at about 50% good; 50% bad.