I just joined this forum and decided to give my two cents for this post, even though it's 2 years old. My WSM runs hot as well, even though I fill the pan with water and am cooking a full packer. I use the Maverick probes and don't look at the WSM thermostat. My smoker temp is usually 250 degrees even though most vents are barely open. I think the problem is too much charcoal.
Having said that, my brisket turns out pretty good. A good tip if you have dry brisket (usually the thin portion of the flat), cut it up and soak it in the au jus that you hopefully saved if you did the Texas Crutch. That'll help remoisten it quite nicely!