Ongoing vibration issue

I'm for changing out the aftermarket mounts. I've heard before that a poly trans mount will cause vibration. It is about the only thing left besides the trans, and I doubt that is it. I was having a vibration in my truck, and I talked to my transmission builder, and he said that there's nothing in the transmission to vibrate. It turned out to be a bent flexplate.
Not to hijack the thread but it is all relevant.
Which auto trans do you have?
Have you tried using a factory tail housing counter weight?