In my quest to try and locate the source of my 2nd gear vibration (20-25mph), I was reviewing my transmission mount change. Not sure if I was clumsy and forgot something, but I already checked the service manual and can't find whether or not there is something that goes into this hole behind the lower rear transmission mount. I've already double checked the sizes of the bolts that go in (correct), so I don't think that I'm using a shorter bolt...

Transmission mount
Hole behind transmission mount, right under CV axle