95 Roadmaster noise, vibration in rear

Got a lot of noise and vibration in the rear portion of the vehicle. Excelleration is normal but when the vehicle comes down to normal speeds it starts to vibrate and shack the bagebers out of the vehicle. Step on the gas and the vibration goes away. Anyway I am presuming it will be the U-joint/s. Have to put it on some jack stands to check maybe this friday. Are these U-joints standard or are they going to be different. Any special tools needed? Anything else I should look for while it's off the ground. Other rear end checks? Constructive comments always welcome....
Thanks Guys
GT

Check the pinion bearings. If there is play in the yoke, there is no longer any preload on the pinion bearings. That's a pretty involved job, but worth saving the 8½" axle.

Check the pinion bearings. If there is play in the yoke, there is no longer any preload on the pinion bearings. That's a pretty involved job, but worth saving the 8½" axle.

Thanks Bowtie: I don't have a manual but when I get it on jack stands I will be able to check everything out. If it is the ring and/or pinion gear, I will need a manual. I have not done the preload shim stock deal on a rear end in a LONG time. So I will need a manual and a boat load of help from the fine folks here. Once I do some troubleshooting will be able to pin point the help needed. I do have shop and the time to do the job right.
Again, Thanks Bowtie

Check the pinion bearings. If there is play in the yoke, there is no longer any preload on the pinion bearings. That's a pretty involved job, but worth saving the 8½" axle.

OK BOWTIE;
Here we go. The Buicks on stands. When I start it and put it in drive there is a noticable clunk noise in the rear. Then I put it in neutreal and the noise goes away. Shift it to reverse and here the clunk again.
I stopped the car. Got out and grabbed one of the rear tires and rolled it forward and backwards. You can here the faint clunk noise. While under the vehicle I looked at the U-joints, and drive shaft. U-joints were tight with no play. There was a very small leak at the transmission tail shaft seal, but not the problem. The tranny fluid level is good. I also tried to wiggle both rear tires up, down and side to side. To check for possible wheel bearing problems. No wiggle. Last thing I checked was the oil level in the rear end. Good.
Any comments on what to check next while it's up in the air?
On another note, I now have a SQUALLING pully. Found it with some spray lube. It's the pulley below the alternator and above AC compressor. Any idea how to pull this thing.
Any more problems and I think I'll put a bullet thru the block:crying:

Again Thanks Bowtie

If the input pinion has no noticeable play, there may be a problem with the differential gears (spiders and side gears) or ring gear clearance. It might be time to open it up and drain the old gear oil then take a good look.