Move the lower brisket to the top every hour..
Wow, doesnt that increase the cooking time by 15 minutes EACH time you
take the lid off ?
Remember, the heat must rise again.
If i were you , i´d try to get a second grate in and put that a little over the lower brisket.
Then swap the meat from the lower to the upper grate every 2 hours.
You get a much faster cook that way and a better smoke penetration..
Just my 2 cent, based on my experience with my weber smokey mountain cooker.