Ram transmission issues

I have a Ram 4500 6.4 4x4 Laramie crewcab with a
12 foot flatbed in winter we seal with it in winter
we plow. Last night i noticed all the shift position
letters were green and it was saying it was stuck in
reverse . But it wasnt, seemed to be shifting hard
into gear when it was doing it. i could shut truck off
it would reset all the letters are lit white as usual .
Id start plowing and it would start doing it again.
My transmission temp reading is all over the place
one second its 189 then jumps to 300 then down
to 125?