Sounds like you have just the flat portion of the brisket. What are you cooking it on? Any pics of the cut? My suggestion would be to smoke for 3 to 4 hours (or once the IT of the meat reaches around 160) at 225-250, then wrap in foil or foil pan, with a cup of liquid (beef broth, favorite beer or even a Coke or Dr. Pepper). Place back on the smoker or even move it to the oven, keeping the temp constant at 225-250, once the IT of the meat reaches 195 degrees, start checking the brisket for doneness every 5 degrees of IT gain afterwards, by simply using a toothpick and inserting it into the meat, once the toothpick slides in easily, with a feel like butter, it's done. Once you pull the meat from the heat source, vent the foil so that it stops cooking for about 15 to 20 minutes, then rewrap in foil, careful to save the juices from the cook, then wrap in a towel or just place in a cooler. Allow the meat to rest for at least 1 hour, longer is preferred, then slice across the grain and serve. Save the juices so that if it does end up a bit dry, just drizzle the juices over your slices or soak them in a pan of the au jus to bring it back to life. The au jus is also great to cut your favorite sauce with to accompany the brisket for sammies and such. I cut Sweet Baby Rays 1 cup to 1 cup of au jus and heat for a wonderful brisket sauce. The au jus also comes in handy for packaging up leftovers, keeping your meat nice and moist for the next time you eat some.
Hope this helps...happy smoking!