I have an 89 Chevy 4-wheel drive, 1/2ton pick-up with a 700-R4 transmission that has about 3,000 miles on it. The other day I pulled a small tractor and on the way back I developed a vibration about 55mph. I then pulled the drive shaft, put it in gear, and still had the bad vibration. I replaced all u-joints. I pulled the transfer case off, and still had the vibration. But, when I call the transmission shop, they told me you have the transfer case on, or it will vibrate. They said it was probably my torque convertor. I put a brand new one in it, and it still vibrates. Worse than before!! I un-bolted the torque convertor, and it stops! Has anyone ever run into this problem before? Any help appreciated! I'm trying to sell it, and no one wants a vibrating truck.