Hi Gerrit,

Welcome! It's been a while, but I used to visit Cape Town, Jo-burg and (mostly) Port Elizabeth a couple of times a year on business. I miss the country, the food and the people.

I'm fighting a similar, but different problem. I think I've figured mine out, but haven't tested the theory yet. Some of the opportunities for vibration that I've considered may be helpful to you:

1) How many miles or kms on your rig? Does the rear driveline have a slip-yoke into the t-case like our older Pajeros? If so, is it possible that you have wear on the yoke splines that was corrected by the swap to the other prop shaft?
2) Have you cranked the torsion bars? Drive line geometry is affected by changes in both front and rear frame height. The higher the truck's frame height above the axle (in either front or rear) the more pinion angle to t-case angle is aggravated. Have you checked the drive angle relationship? The fact that the vibration dissapeared after swapping propshafts would lessen the possibility that drive angles are the problem, but there could be a slight difference in the U-joints abilitiy to handle the angles.
3) Several owners here have had bad luck with inexpensive U-joints. I suspect it's because of the normal driveline angles on the factory setup.

I can't say any of this will be the problem, but offered as food for thought.

Good luck,
Frank