Quest (2007) Transmission - Jerking (when downshifting)

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Bought a 2007 Quest 2 years ago with 95K. Now has 125K. The condition over time was getting worse - When the car was fully warmed up, and especially when in stop and go traffic (local roads) when slowing down, as soon as the odometer hit 20mph, the car would (most of the time) jerk pretty badly. The fluid was black and smelled burnt. I did 3 drain and fills over the past couple of months. After the last one, where the fluid seemed to look normal, it was driving beautifully for a few days and then started to act up again (as above).
Has anyone dealt with this? Any suggestions?
Thanks in advance!
Eli