Are you sure about the thermometer and its placement?
Close all 3 bottom vents and let it settle back down. Usually temp changes with the vents take about 10-15 to take effect.
Windshield = Good
I think it was already mentioned, but once you start creeping up on 200, close the vents to 1/3 the way.
My WSM runs stock (door), pretty much with 1-2 mm vent openings. Dont worry it takes a bit of practise, but soon you'll learn how to dial the WSM in to almost any temp you want.
Open to raise temp
Close vetns to cool
Then you'll have your "Steady" vent setting to hold temps
EDIt: Also the first few times I ran my new WSM, especially with Lump, it ran hot (260) and I had problems getting it down. After more uses it seemed to "break in" and works perfect now.