Wrangler 1992 Vibrations at 80KMs

Help please! I have a 92 Wrangler, when it hits 80kms the car vibrates. It sounds like it is coming from the transfer box but I have replaced all joints and drive shafts. When Main shaft from the transfer box to the front Diff is removed the vibration stops. Does this shaft need balancing or is it not staight. When driving without the shaft and putting the car into 4 wheel drive there is no noise?

Many thanks for any suggestions

Jackal1