overheating when turning off car

Not using the shroud is probably why it overheats idling. When idling there's no air flow without it. Going down the road you get plenty of air flow so it don't overheat.

Is the temp sender screwed right into the head? If so it's heat soaking when you shut it off causing the gauge to go up. Does the gauge go right back down after you start it? If so don't worry about the heat soak. It happens on all vehicles but most have the sender screwed into the intake so it doesn't go up after you shut it off.