with both my 93s i had a bad vibration with poly mounts at certain speeds. switched back to stock and no vibration.

 

I put a poly trans mount on my 96 LT1, added vibration was minimal. Guess my drivetrain was in sound condition then.
If your car gets the shakes, the poly mount isn't your problem, it's just helping to amplify a symptom.
Still, in all fairness, can't really compare what to expect or not with an LS1 based on how an LT1 or V6 reacts.

 

Come on, you're comparing vibrations of a 3.4L to a 5.7L?

 

Well, if a 3.4 doesn't vibrate much, neither should an LT1 or LS1. The 3.4 is prone to give off more harmonics than the V8, which is why those cars had a split driveshaft, to dampen the vibrations that would/could otherwise transfer to the back.

 

And mine has a single piece. Still no bad vibrations...

 

I am just concerned that if I find the issue being maybe a warped flex plate or out of balance Torque converter that it may be to late. I am afraid I may have to pull the motor down and redo the bottom end from the excessive vibration on the crank. I just bought the car recently and the Transmission was rebuilt about a year ago so it very well could have been doing this for a year or more.

My next step is to unbolt the torque converter again(even tho i just put permanent lock-tite on) and run the car to see if its engine vibration or transmission.

 

Make sure you slide the torque converter into the trans as far as it will go (there is play) so that it's not dragging on the flexplate when you run the engine.

 

Thanks Camaro 69, will do and I will post results.

 

look for any part of the motor or exhaust that is against the frame. my oil pan was against the steering rack and untill i replaced a badly saging motor mount i had a pretty good vibration.

 

Okay so here is my update for you guys!

I pulled the starter back off and loosened the Torque Converter bolts off, I then pried the TC off the flywheel and reinstalled the starter. I started the Car and brought it trough all revs from idle 1200rpm + or - up to 5000rpm and NEVER once got a Vibration! So it is defiantly the Transmission! My next question is I am just going to assume the TC needs to be replaced but what else could cause this heavy vibration in the Transmission besides the TC? Please keep in mind the Tranny was rebuilt 20K miles ago and has had some pretty beefy upgrades.