The difference between dome temp and top grate temp can be 30 - 40 degrees, so if you are reading the temp at the dome and it is 200, your top grate may be as low as 160! The brisket will never be done if that is the case. Check you fire to see how it is burning. You'll probably have to add both unlit and lit charcoal as Mark suggested to get the temp up and keep it going long enough to finish the brisket.
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