[Greenhornet2]

Does the vibration get worse as you apply power once you are at the speed the vibration occurs? Going the same mph, does the vibration have the same speed or intensity regardless of what gear you are in? Still sounds like driveshaft to me. Is there any play in the cv shafts? It's really hard to diagnose something like this without experiencing it first hand. It's not in the engine or clutch if its speed related and not rpm related. If the vibration stays the same regardless if you are in 4th 5th 6th and is more speed related you are looking at driveshaft, cv shafts, or possibly diff. Doubt it's the diff but you can put the car in neutral and see if you can move the pinion.