Hey Monkeybomber! Your flank steak like brisket was due to inadequate cooking time. I started my first real job at a BBQ restaurant when I was 13. Worked there until I was 18. I'm no expert but I did learn how to cook BBQ.
Here is what I recommend...
Apply your rub and refrigerate for 12 hours. Put the brisket(9 1/2 to 13 lbs.) on the smoker fresh out of the cooler. When you start the brisket your temp should be no higher than 275 F., cook the brisket for 12 to 14 hours and never let the temp get higher than 325. I have cooked at least 20,000 pounds of brisket with that method. For ribs do the same thing except you only cook the slab for about 4 hours.
Tip: after you cook the brisket, place it in a tub or large pan and add a few inches of water. This will keep the brisket from drying out and the real benefit is when you pour off the liquid. Save that liquid and put it in the fridge. The next day, remove the hard fat from the surface and you will have some beef jelly remaining. Man! That stuff is awesome to add into a homemade BBQ sauce. I have nade thousands of gallons of sauce 55 gallons at a time using that stuff.