Also you said you leave the top off until you get some temperature ?? I never leave the top off when doing anything with a UDS....when the top is off it is an uncontrolled burn that usually leads to a temp spike when the lid is replaced.
Another thing with lump......you need to get it tight together, the first few times I just dumped in the basket and got uneven burning...now I just shake the basket while twisting it to settle the chunks together.
A couple pictures of the whole rig might be worth a few thousand words of description :-).
If I had to guess it would be that the intake holes being up that far from the bottom is the problem, but I'm an utter noob at UDS construction myself, in my limited experience too much exhaust (poor fitting dome lid) the temp ran away hot.