I see a possible transmission rebuild or replacement in your future.

A lot of people on here have had to do that shortly after a transmission flush, if the transmission had not been flushed on a regular basis.

Change oil and filter - fine no problems.

Add a flush and it stirs up all the old varnish that was safely hidden away in all the nooks and crannies. Then the varnish clogs galleries etc, and bingo, you are up for repairs.

I hope I am wrong.

PK