Strange, mild (transmission?) jerk issue
 

Hey gang,
I have a 2000 e-150 conversion with the 4.6L triton v8 with only about 90k miles (but some were towing, and looks like it was in a salty part of the country for quite some time). I've only owned the van about 6 months.

If I'm slowing to a stoplight and ease off the gently, or starting from a stop and accelerate gently, it's generally fine. It doesn't happen very often, but if I'm slowing down and pull my foot off quickly, there's just one little jerk, almost as if while I'm slowing down (maybe around 15mph) someone taps me from behind lightly.

This has happened just for a few weeks now bug I don't want to ignore it. Drives fine other than that. I thought the fluid looked a little low so I added a little bit, just several oz, no change. Fluid looks/smells like it's in good shape, but could easily be original.

Any help or pointers is greatly appreciated!