Recently I experienced and over heating issue with my 2013 JD Gator 855d. This problem occurred after a day in the mud. I took the gator home and washed it well. I used a pressure washer.
I changed the obvious things like the thermostat and heating sensor. The over heating light still came on only when going up large hills. After talking with the service department, they said more than likely they would not be able to replicate the issue.
One day after using the gator, I washed it again and spent more time washing the radiator. The radiator was packed full of mud and could not be seen after washing the 1st time.
In my opinion the radiator should be more accessible and easier to clean. After taking most of the front end apart and cleaning it well with the pressure washer, Im thankful the problem is solved.
I wanted to pass this along to those that may have the same issue.