That's not your issue. If it was assembled improperly, you'd have a slight buzzing vibration, at all times, that gets worse at higher speeds .........nothing like your current, intermittent symptoms.

What's the deal with the trailing arm bushings? Have you replaced those? It sounds like the entire wheel is free to occillate around the vertical axis by 3/8". I think you'll need to take care of this situation first.........if simply to rule it out.

I've got difficulty accepting another center bearing failure in such a short period of time........