2002 rodoe ls 3.2 l.

Sometimes while driving on alot of hills or pulling boat my temp light comes on.
If i drive in 3rd while pulling my boat the light does not come on. i recently change fluid and its was dark red but i do not know the history of fluid changes. just went over a 100k on rodeo. so i change fluid it didnt smell burnt just dark red.

Anyway my question is does it sound like a oil cooler problem is this common because the rodeo trys to shift into overdrive alot and back to third. Im going to change the fluid soon again just to make sure I got all 9 qts out and fresh fluid.
Car drives fine. and no hard shifting