My trans mount resently failed in my GTX when I was out thrashing on it pretty hard and it had a bad vibration at different rpm ranges in nuetral and a drone at highway speed (sounded like a out of balance drive shaft) dropped in a new poly mount and it's quiet and smooth again.
Same thing happened to me a couple of years ago. Took me a while to piece it together, but sure enough... trans mount was bad. Much better now.
