If you feel as though it is your driveshaft then I would say to just pull the driveshaft and rotate the joints by hand. That is what I did when I was doing my clutch. It is a very simple job to remove. Both of mine were shot at 120,000 miles. I found a driveshaft shop that can machine out the yokes, replace the joint with a greasable version, and then spin balance the assembly. They are located in Shrewsbury MA. Mitchells driveshaft service.
Are you sure the tires are balanced good? A weight didn't come unstuck from the inside of the rim?