Driveline Vibrations

[Tarheel]

For some time I had this slight vibration that would come in at maybe around 110kmh.
Last week I had new unis put on the drive shaft and the thing rebalanced.
After fitting the driveshaft back into the car and then taking it out for a drive, I noticed a vibration at 70kmh and 80kmh. The vibration is slight, but noticeable and annoying, especially on a smooth road. I am assuming they have stuffed up on the balancing of the drive shaft, but how can they get that wrong?
When I am doing 80-90kmh and push the clutch in, I feel the vibration too. Maybe even worse initially and then it phases out.
Tyres are all balanced and wheel alignment done. 
The vibration is definitely worse since the drive shaft was done.
Is it the drive shaft, or is it something else?
The engine is a 289 with a top loader.

[shaunp]

Is the tail housing bush in the gearbox ok.?

[Tarheel]

As far as I know... Yes

[big al]

What wheels do you have?

Al

[unilec5544]

Probably a good idea to have the drive shaft balanced.

[barnett468]

Probably a good idea to have the drive shaft balanced.

[Tarheel]

I think I have fixed the issue, or the worst part of the vibration. I saw somewhere a discussion about undoing the rear yoke, dropping the rear of the driveshaft out and rotating it 180 degrees and putting it back. I did this and made sure to not over tighten the u-bolts.
Took it for a drive and it seemed much better. Odd I know, but it is what it is...
Thanks anyway

[evan]

I think I have fixed the issue, or the worst part of the vibration. I saw somewhere a discussion about undoing the rear yoke, dropping the rear of the driveshaft out and rotating it 180 degrees and putting it back. I did this and made sure to not over tighten the u-bolts.
Took it for a drive and it seemed much better. Odd I know, but it is what it is...
Thanks anyway

Beat me to it! I went through this years ago after having my tranny rebuilt.

Evan.