Sorry, didn't see this in time, but for future reference here's how my papaw taught me how to cook a brisket:
Rub salt, pepper, and garlic on your brisket and cook it low (275-325) pretty much all day. 6 hours minimum, covered. Then take it out of the oven, and stick it directly in the fridge overnight. The next day slice against the grain, fairly thin (not paper thin, but you don't want chunks either). Then you lay down in a roasting pan a layer of your favorite bbq sauce, thinly sliced onions, salt, pepper, and more garlic, a layer of brisket slices, and repeat until you run out of meat, top with sauce & onions, recover, and stick in the oven at 350 for about an hour. Basically you're reheating and melding flavors here... It's pretty good. We make our own bbq sauce so it's never the same, but any kind works.