I also use a big block and it really is almost set it and forget it. But I'll tell you, I really don't know why they put those thermometers in the door. In my experience, they are notoriously wrong. Mine was reading about 35 degrees cool. But more to the point. The answer to your question depends. What was the temp of the meat when you put it in and most of all, what is the temp of the smoker. Don't trust the door thermometer. But, in my opinion, the internal temp of the brisket does seem to be high for the amount of time it has been in the smoker. As a suggestion, if you trust the accuracy of the therm in the meat, (can be tested with the old boiling water trick) pull the probe out of the meat and put it through a small potato for stability. Then place the potato on the grill to check the smoker temp. Just be sure the probe is all the way through the potato so that the sensor on the tip can accurately measure the temp. Then, when you are satisfied with the temp of the smoker (relative to the door thermometer) you can replace the probe in the meat.