Yeah. What they said. You probably haven't waited long enough. Brisket, when cooking by time, is done when it finishes cooking. Aim for a particular cooking temp; I'm always aiming for 240. Most people pull the brisket to put it in foil in the region of 170*. I've seen posts and suggestions that have briskets foiled as early as 140*, which is when the smoke ring stops forming. Make sure you trim as much fat as possible so you don't spend time cooking it! Kid Curry posted a great link about competition cooking from the Pickled Pig team website, where they break down, to recipes and precise steps, how they prep chicken and briskets.
Gee, I'm running off at the "mouth" again. Imagine that. People are shocked.
Welcome to our smoky corner of AZ. Hope to meet you at some events. This is a great group of people. A great group of DAVES, too! WOO HOOO, We got another!!
Dave