Trenton oliver

2017 gmc sierra 1500 5.3 6 speed and 75 and just driving normally trucks all stock put a new transmission in last may. When new transmission went I put a new updated thermostat in

So out of nowhere today i decided to look at my trans temp and it was at 230 degrees and went up to 240 then cooled down. I was wondering before i take it to a shop to get anything done. What could be causing this it’s still shifting smooth has butter with no issues.