Couple of weeks ago, I posted about this horrific vibration I have been getting from the rear of my Dakota. Well, it spent 3 weeks at the dealer, 4 days of that being diagnostic time alone. The ordered and put one drive shaft in. Well tried to, parts depot shipped the wrong drive shaft. So they had to order a new one, too bad my Chrysler Ext. Warrenty wouldn't pay for a custom one to be built, it finally arrive on the 24th and was installed. The vibration is still there, but now it's more centralized in speed. Before, you would notice it above 25 mph, and get horrible above 60 mph. Now, it doesn't start to be noticed until speeds above 45 mph, and gets bad again above 60 mph. So this morning, I had all 4 tires replaced, this appears to have corrected much of it. Didn't notice anything on surface streets, haven't had a chance to get on the highway with it, will do that later today. But, one thing I did notice, the old tires all had 2 to 4 weights per side for balancing, the outside of each of these only has one weight, and the insideonly had two on one wheel.

 

Tires cause alot of problem. I had 38 inch tires on a chevy blazer and at 55 the darn truck would start to really make noise because of the balancing was wrong. I ended up sells the tires and going back to 33 inch tires and had them balanced at a truck place and never had many more trouble with the truck and the noise. I did like the 38's but the gas gauge moved way to fast with the darn things on there

 

I hope your problem is solved but I'm wondering what the highway speed test will tell. After a suspension lift, I chased vibrations on my 97 Cherokee for weeks. Changed both driveshafts, new u-joints, rebalanced tires (new Michelins), lowered the T-case, etc, etc. Finally, since the vibration felt like it was mid-vehicle and back, I put it on jack stands with rear tires on and ran it up to 60 (there was the vibration). Then I took tires off and repeated the test (vibration still there). So I knew it had to be driveline. I rotated the driveshaft 180 degrees in the rear yoke (that helped some). Then finally tried shimming the rear axle to equal angle at u-joint at front and rear of driveshaft. That did it. I know its a long story, but if the vibration is still there at highway speeds, you might want to try a wheels off test ( carefully) to see if its driveline. Also, regarding weights, I've seen the same thing. Heck, one of the 33" BFGs on my Dak balanced out needing no weights at all. Another one took a strip about 6" long!
Good luck and keep us posted.