I would take Z's and YB's suggestion's about not rushing a brisket, or anything else in the smoker, for that matter.
But, if you were going to trim = cut, a brisket for some reason, you would want to remove meat from the thin end. The reasoning is that you would want to try and make the piece of meat as uniform in thickness as possible, which will result in it cooking more uniformly. YB2
I was typing this post while you entered your post above, didn't realize it was such a large brisket