Chevrolet Repair: Vibration, hose clamp, wheel balance

Question
Mark I own a 1986 Starcraft Van (excellent shape - new engine, trany and diff.) I have a vibration- and have for years -when the vehicle hits 65 KM/40 Mph and at 105 KM/ 68 mphr. It is like the rur rur vibration that a V/8 makes if you sit and listen to it.  I have done the drive shaft balancing etc. three times, had a spring company check the driveshaft angles.  When I hopped the engine up I asked the installer to change the engine mounts. He said they were okay so he never.  They have been in the chassis since the truck was built - 17 years. Could they be so solid that they transfer the vibration up into the cabin. The vibration will vibrate the outside left mirror enough to fizzle the image/ not on right side.  Wheel balance is perfect.  This has been bothering me for 10 years and has become an obsession to find it.  Thanks in advance for any advice or tips you can give me.
E/J

Answer
Hi Earl, This sounds just like a driveshaft vibration. I have sent out driveshafts 3 times and still had to balance them in the truck. To balance them in the truck you have one person run the truck up to the speed it vibrates and the other person is under the truck with a hose clamp and a weight. You keep stopping to move the weight until you find the spot the weight is needed. This takes some time to do. you don't know where on the shaft to put the weight and you have a 3 piece shaft.

      Let me know how you make out         Mark