I have 3 intakes on my UDS also; 2 are elbowed with an 18 in vertical pipe and each have ball valves at the top. I usually keep the 3rd one uncapped and throttle my temps with the ball valves. I have seen mine go as high as 330F when testing it out. I usually fill my basket with lump and use briquettes from the chimney to start it up. I've maintained temps of 225-260 for maybe 16-20 hrs tops. I think I would try more fuel in your basket first...
"Just keepin' it GRILL"....on an Ugly Drum Smoker!