No updates for a while. We had a small vibration, not really bad, just annoying, and of course right at 65-70 MPH. When my wife drove the car we had the 3.07 differential in it, one attempt at finding the vibration. We put the 3.73 back in (whole chunk, nothing is shared between the two). And the vibration came back. Drive shaft out, re balanced, re tubed, trans out, looking for something, anything that may cause vibration. Half shafts out, again. Trans UP diff, down to get angles better. They were not far off before. All in attempt to cure this vibration.
Called a local guy I know, who does a lot, I mean a whole lot, of Ls stuff. He said "poly mount", I said yes. He said swap it out for a rubber one. Thought he was CRAZY, we have built a ton of cars with poly mount. Well, we were dead wrong. There is a whole thread on LS tech about poly mounts. Like 5 pages. Apparently T56 transmissions are very pick about the mount used on them. I have it on the lift with half shafts out, and the vibration appears to be gone.
Not complaining about anything just trying to help others that may run into a problem. 3000 miles fighting this vibration, hope it is gone for good. R