Does this look like its bad enough to cause my mystery acceleration vibration?
The rubber feels pretty soft.

 

It looks pretty good, check the crossmember to make sure its not cracked. Accel vibration is not usually a trans mount, that sounds more like U joint or carrier bearing( although the carrier looks new) make sure all your U joints have angle to them and arent straight or they will vibrate and wear out quicker. Trans mounts usually give a knock when you shut the truck off if they are bad

 

I've replaced he carrier bearing, and pushed / pulled all he universal's, no play in there.
What its doing is under normal acceleration around the top of first gear andinto second fear the whole truck starts to shake like km drive over a badly washboarded road. 5 times worse than hitting rumble strips at low speed.

I'm starting to wonder if its from inside the tranny.