I agree, the buildup is likely not the problem. I'll get a rough heat map this afternoon when its seasoning - I've got 6 ports lined up for sensors (2 12" analog, 4 stoker) plus the vent in the lid.
My suspicion is that the convection inside is going to give you warmer air in the center over the fire, cooling on the food/lid and dropping down the outside. (That would also explain the condensation some people are getting on the lids - a pretty big temp drop when it hits the top..)
You could defeat that a little with something like a pizza stone, and still get the 'burnt juices'. I'm going to give it a try - it should heat up enough to sizzle, plus pushing the hot air to the walls so it mixes better.