Sorry Question went around recently with not much luck..
  http://www.dubaipetrolheads.com/car-chat/transmission-vibration-(rear-propshaft)-2001-wrangler/

ABB in Al Quoz might be able to help, but not sure they deal with general public (another Turbocharger / big industry place).

p.s. Did you witness the balancing ?
For the Turbo's at work (ABB) I get mean, once balanced I make them add a temporary weight spin up it should then be out, remove the temp weight and re-spin again and should then be perfect, if not the machine if FTFF or the result was a flog.

rbailey - Was there when they did the initial spin up... was out by quite a bit. They then welded on a few weights at one end. Had to leave before the welding was done but when I went by in the evening to pick up the driveshaft, they had the report from the balancing and it appeared to be close to spot on. The balancing had made a difference (vibrations started at 110 km/h before, now it starts just below 120 km/h, stops just above & then starts above 140 km/h). Had no vibration issues with the stock driveshaft. Do you know anyone who I could contact at ABB to enquire about the balancing?

axehead - I know someone who's been to Trinity to cut a driveshaft. He was told there's no guarantees about the driveshaft's balance after that and that Trinity do't have the capability to balance them.

Sorry 2 jump in but the other question might be:

what else did you change..?

kr  D.

ok good... you measured/adjusted the drivetrain angles too I guess?

-D

Hm, well, of course it <can> be that it's just...alloy. It's lighter and that means the resonances (which are always there, balanced or not) move up the frequency range, i.e. perhaps from where you didn't notice them on the old shaft, to where they are now...  If that's the case, nothing will really 'fix' it. Any stiffer bushes anywhere just make it worse of course. That's a normal 'modified car' NVH issue...

Other things worth checking, if u haven't 3 times already:

The UJ bearings are ok/free, no sticky spots (presumably they were new anyway, but still...)
The prop/front yoke are together the same length as the old, and the engagement at front is to the same depth in the splines...
Presumably this ain't a '68 Muzzie , so the fit of the splines shouldn't be an issue (they loosen with wear..).

kr  D.

Is the wrangler lifted? Sometimes with the SWB wrangler you need to drop the gearbox to align the shaft angle back to the rear diff when it is lifted.

The less complete lift kits may not sell the spacers that drop the cross member.

Any progress with this?