Since I installed my 14bff and my "new" driveshaft in my 'burb I've had a very annoying vibration. I installed the 14b first, I drove it almost a week with the stock shaft that was now 2" too short. I did not feel a vibration then, but I never got it on the interstate like that either. I then took a driveshaft that was 2" too long to the driveshaft shop and had it shortened to my desired length, but they did not balance it. I installed the "new" shaft and went for a test drive. I had a terrible vibration from 40mph-up, so I pulled it back out and took it back. They balanced it and said that it required 1.5 oz. of weight, 1 up front and .5 at the rear, both were opposite of the factory weights. I re-installed the driveshaft and took off down the road and all was well.......so I thought. We took it out of town and pulled my 16' trailer with 3 atvs on it to LBL 200 miles away. At 55mph and up I still had a vibration, not nearly as bad, but it was noticeable. After driving it 400 miles like that I had to replace both the TC tailhousing seal and my pinion seal. So, once again I pulled the driveshaft out and sent it back to the shop with my wife, as I had to work. They checked it again and said it was perfectly balanced and had no bends in it. The shaft has new Spicer joints in it (1/2ton to 3/4ton in rear). I went by my local tranny/diff. shop to see what they thought and they said that a bearing would have to be chewed up pretty bad in the rear diff. to cause such a vibration, and I checked all of the bearings before I installed the rear end. I almost forgot, the sound/feel of the vibration changes with accelerator pedal pressure, if you coast it makes a louder noise and if you let off completely it changes again. Any ideas? This is not a tire vibration, it's too "fast" for that. I do have 4" of lift and 33's.