I ran a Prothane trans mount with stock motor mounts on my old 97, and now on my 01. The vibes last about a week or two and smooth out a lot. I also added a poly torque arm mount, I get some vibes at 80, but it's not horrible. I never got on the highway in between the trans and TA mount, so I can't tell you which one is the cause. I'll do some poly motor mounts within the next year anyway. I'll never use a stock trans mount again. The solid shifting is more important to me than a tiny vibe.

And I've NEVER heard of anyone breaking a trans when using a poly trans mount/stock motor mounts.

See this thread I made too: https://ls1tech.com/forums/general-m...ly-mounts.html

 

Thank you.