Never use synthetic in our transmissions. You did the right thing, so we'll move on....
At this point, it looks as if something got dislodged during the temperature and fluid cycling. I'd be tempted to put some Seafoam trans-tune in there for a week or two, then have the whole system professionally flushed. There is some risk involved, rare cases of this making it worse, but at this point, I think it'* a good option for you.
I have mine flushed regularly once a year, and the car always liked it.