Neil -
I'll have you over next time I do one, but it's really about your cooker. Your pit temps as others have suggested, seem too high based on the characteristics you're describing. I wrap about 2 inches of the flat after about 3 hours, assuming cook temperatures in the 220-240 range. Move the meat like Phil says, foil what you have to, quick baffle/heat shield mod, spray the meat occassionally, and smaller fire. You do not need a big fire. Also - I don't remeber if you can add fuel through the side of your cooker or if you come in through the top.