2001 300 transmission shifting issue

[266mopars]

Got an issue with my 2001  300"s transmission Sometimes it wont shift and it will run at 3 to 3.5 k rpms @ 40-45 and if you pull over  and turn it off it will be fine It did it a few times over a few months now its every morning is there some sort on sensor that can be replaced.It seems to work better if its warmer out ???fluid is fine shifts perfect when restarted.Anyone have this issue Thanks for any suggestions