Place all of the barbecue sauce ingredients in a 3-quart or larger slow cooker and stir to combine.Place all of the measured brisket ingredients except the brisket in a medium bowl and stir to combine.Place the brisket on a cutting board and cut it in half widthwise. Evenly coat it with the spice rub and place the 2 brisket pieces in the slow cooker. Cover and cook on low until fork-tender, about 10 hours.Transfer the brisket to a clean cutting board. Pour the barbecue sauce from the slow cooker into a medium heatproof bowl and set it aside.Remove the excess fat from the brisket and discard it. Slice the meat against the grain into 1/4-inch-thick pieces and return it to the slow cooker. (Alternatively, you can shred the meat with 2 forks.) Use a spoon to skim and discard the fat from the surface of the barbecue sauce. Return the sauce to the slow cooker and stir gently to combine it with the meat. Taste and season with salt and pepper as needed.