re: What am I doing wrong?

No way was it 180 in Six hours. I wrap at 5 hours in butcher paper and insert a remote probe way into the flat. Depends on the size at what the temp will be, I trim Briskets to 1/4 , rub with salt pepper and Worchester sauce and let them sit over night refrigerated. I also let them sit at room temp for four hours before putting them on. (This cuts cook time by hours) slice grain and serve as you are slicing