After three years of friggin around I fixed my vibration problem!!
I bought a LS1 driveshaft thinking that would fix my vibration. When it didn't, I assumed that the driveshaft couldn't be the problem and started looking everywhere else.
https://www.thirdgen.org/forums/tran...heck-list.html
After an extensive search this summer I concluded both the steel shaft and LS1 shafts must be bad. I sent my LS1 shaft to Dennys Driveshaft http://www.dennysdriveshaft.com/
He told me it was no good and built me a custom steel shaft for $350. ($400 with tax and shipping)
Problem solved. I've had it up to 120 with 4.10's, no vibrations.
$350 sounds expensive, but I bought the LS1 shaft used $160 shipped, 60 bucks for joints, $20 for a local truck shop to check it for straightness and balance (it tested good for them.....they didn't spin it fast enough) So i had $240 in a shaft that I had to throw away. Looking at it that way, $350 dosen't seems so bad for a custom made shaft spun to 6500rpm.....

 

It is good that the vib's are gone. Makes highway driving a pleasure again. BTDT.

Other then stating that the LS1 shaft was no good, did Dennys say why? It would be interesting to know what the issue was with that shaft.

The $350 for a shaft isn't bad. When the '92 was new it was fine on the highway. Sometime between 40K and 60K miles a vibration started to set in. By the 60K mark it was real bad. Purchased another steel shaft with about 42K miles on it. Much better, but still a hair of vibration. Then as the miles racked up the vibration got worse (real bad).

At that point I purchased a new GM 2000 MY Camaro aluminum driveshaft. Wow, no vibration at all. I think it is even better then when the car was new.

RBob.