can you torque a driveshaft bolt or rebalance the driveshaft to stop vibration?

What is your question?

My 2003 Toyota 4runner is vibrating in the rear between 30-35mph but the vibration goes away @ 40mph and above. If I try these 3 things could this improve or fix the problem. 1)grease u-joint fittings. 2) rebalance driveshaft. 3)torque driveshaft bolt .Can anyone think of anything else? The feeling is as though one or both of the rear tires is vibrating in a vertical motion like dribbling a basketball extremely fast and low to the ground. There are no leaks and no other noises and the vibration is fairly mild.

What makes this problem better or worse?

better when speed is increased

How long has your 2003 Toyota 4Runner had this problem?

months