The only way to control temps, when you add more wood is by reducing the airflow through the cooker. As Jewc75 shows, a ribbon type fire is easier to control because you don't have to keep opening the box to add wood. Next time you do a butt put a good rub on it, I can offer a good recipe if you like, wrap it in saran wrap and let it sit in the fridge over night. Get your fire and your smoke going and stabilized at 225°-250°. You want your wood smoke a blue color not white, which you get when you first get the wood started. You don't really need much wood smoke after about 2 hrs into the cook because the meat has absorbed most of what it will at that point. Soaking your wood is pretty much a waste of time
http://amazingribs.com/tips_and_technique/mythbusting_soaking_wood.html Just use it dry. Let it cook at the 225°-250° until it reaches 195° in the thickest part of the butt. Pull it off, wrap it in foil, then some old towels and put it in a cooler for at least 1 hr. It will be good in the cooler for up to about 4 hrs, so it's easy to have it ready ahead of time. when you take it out of the cooler it will still be very hot and you can pull it to your hearts content.
How long did your cook take? You only cooked it to 180° and that's the internal for slicing pork not pulling pork. I much prefer lump charcoal and I stopped using briquettes a long time ago. Lump cooks at a higher temp and is almost ash less. I got tired of cleaning all the ash out of my cookers from the briquettes.