Oil temp rising

The oil temp on my 7.3 stays around 140 from what the gauge says but after 20 min or so of driving the oil temp will slowly rise to almost 190 when not cruising at about 40. Once I get up and going again it drops fairly quickly. It has fresh oil and is full. I don't think it is an unsafe temp but don't think it's right that it raises like that. Any thoughts?