Any ideas? decceleration vibration

I was reading another post and someone mentioned rear end chatter from not using friction modifier.

Here is my problem. I started having this vibration only while decclerating in 3rd gear and it seemd that it was only when i upshifted to third. If i downshifted to 3rd it didnt do it. Then it was the same in 5th. Now it seems that it does it in 2nd and 4th also.

I checked to see if the bolts on the ujoint were loose and they are tight.

I also had 4.10's installed last summer and it didnt do it directly after the install.

So what do you guys think? Tranny, ujoints, rear end?

clarkjr said:

The u-joints/driveshaft can cause a vibration even if you cannot physically feel play in the shaft. I would recommend replacing the u-joints and have the driveshaft balanced (heavy-duty truck repair shops often offer this service). After a gear change, the d/s spins so much faster than it did before and often a vibration will show up right away.

Another potential cause is too much neg. pinion angle. You did not state if you had adjustable control arms but if so, try adding a degree of two more pinion angle into it (postitive, not neg).

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The driveshaft is an aluminum unit. I have stock control arms. This just started all of a sudden and got worse. It wasnt directly after the gear change. It was a few months after.

I talked to a local trans/rearend and he told me that my problem is going to be either in the tailshaft bearing or the ujoints.

I also asked just out of curiousity, how much to rebuild my tranny if i bought the parts. He said if i buy the parts he would tear down, clean and rebuild the tranny for $60.