Must be a problem with your Taylor if the max reading was 151* and the butt still reached 190*. That feat would be impossible, at best.
Squaregg, do the next butt on 250*, do not open the door, see how it goes. Also, try putting the butt on the lowest rack closest to the woodbox. Keep good notes. Experiment. Have fun.
What was the max temp recorded on the probe through the ball of foil?