5th gen limited, rear end vibration

I've got a 2011 limited with a rear vibration and I'm wondering if someone could help me figure out what the deal is. It happens at slow speeds 25 to 40 and seems to come from the passenger side rear.
I took it to a repair shop who diagnosed it as U joints. I had them replaced and it was still doing it. Took it back and they told me that they had stretched the drive line or broken it somehow. They proceeded to order a Toyota factory driveline and U joints which came as a total assembly. A week later they had it installed and STILLhave the vibration. I tried a tube of shutter fix and and it seemed to have helped a little bit possibly can't really tell haven't put a whole lot of miles on it since then. Does anyone have any suggestions with this disaster I don't want to put a new tranny in this thing it's got less than a 100,000 on it. Any help or suggestions would be appreciated thank you