200-300 miles on recent rebuild.....I did see the tranny apart so I believe the rebuild kit was used & tranny was air/bench tested.Welcome to Allpar. As ATF warms, it thins out. If there are internal leaks at seals, etc., it will show up more (leak worse) when warm than when cold.
Test the line pressure between cold and warm to see if it drops significantly. A heavier bodied fluid, like synthetic ATF+4 may hold higher pressures when warm, despite the internal leakage.
It may also be time for a transmission rebuild?
In discussing with my Mopar buddy's this also came up - nice call! How to unstuck it?It could also be caused by a stuck governor. I had a Ford C6 do that to me. Pressure testing as IC mentioned is an excellent diagnostic tool. Chrysler transmissions have pretty good pressure test points if you have the manual with them called out, and from what I recall governor and throttle pressure test points are both there.