Give up on lump, go to briquettes. Also, post some pictures of your UDS showing the inside, outside, lid and basket, maybe someone will see something that is not quite right.
I will add, my UDS takes more than an hour to really adjust once I open the lid to load it, especially with lump. I generally cook with one vent partially open for 225F and one full open for 250F. 2 vents open and it is going hot and fast, with lump, it will burn out quickly.
The SS Platypus, sails again, to the support of the Vets!
"perhaps...but then again...maybe not..."