Just put 2 inch lowering blocks in the wagon, it looks s**t hot but now when I am at 100ks there is a vibration like a whir whir whir. Could it be my uni joints or might it need a tail shaft balance?

Did you remove tailshaft??

the vibration could be from the harmonic on the front of the tail shaft, i had a vibration in my XR6 @ 120 and found that the rubber in the harmonic was soaked with trans fluid, i replaced the yoke and problem fixed..

No, but it did slip out about an inch while i was puting in the blocks but it slipped forward again when I tightened the ubolts up on the diff.

Will check the yolk tomorrow.

Firstly check for play in the transmission extension housing bush, there should be little or no play at the slip yoke at the transmission. If there is no or little play i would go onto replace the universal joints as now the driveline angle has changed and the position where the needle rollers were worn into the UJ cross has now changed. The harmonic balancer part you are thinking of is actually a Slip Yoke Damper and has nothing to do with the balancing of the shaft, its actually to absorb noise and vibration emitted from the transmission mainly in torque converter lock up. Most shafts do not have a slip yoke damper fitted. Remember to mark the original position at both ends of the driveshaft before removing as it must be fitted back in the same position. There will be a yellow dot on the diff flange that should line up with a yellow dot on the shaft next to the tube weld. With the front of the shaft have the yellow dot facing down and put the trans in park so as the output shaft does not rotate.

Try unbolting the tailshaft and turning it 180 sounds silly i know but if you dont bolt them in the same way they came out it can cause a small vibration.

Sounds silly but check that the tailshaft isnt rubbing on exhaust, other possibility is that the height change may have put the pinion angle into an unfavorable harmonic angle.