Chased down a vibration problem that started when I installed a 2.73 posi rear end in my camaro aobut a year ago. Would start at about 65 and up. Swapped the 2.73 into my TA when I picked up a nine bolt for the camaro over the holidays and the TA started the same vibration/same speed. Because I drive the TA everyday I started working on fixing it. Did a lot of searching here. Replaced rear bearings and axles (had a spare set in garage) and the vibe was still there but a little muted. Everything else had been changed with the swap: tires, driveshaft, engine, CAR. This past weekend I took ten minutes and swapped another set of aluminum drums on the rear (I've got a few sets laying around). Problem solved.

Thought I'd throw this out as I didn't see it in any of my searches.