I ended up modifying my smoker by adding an additional vent. So far, I've not smoked another large slab so it hasn't yet proven effective, or not.
I was almost entirely a hickory guy but as I have a number of pecan trees in my pastures that regularly drop limbs, I decided to give pecan a try. It tastes great, without having to worry about too much, and it has kept its temp. All on smaller cuts, however. I am wondering if the wood makes any difference...