Vent in lid should always be full open. period. The design of a UDS is to go low. i cruise at 250-275. I can get it up to 350, and i do frequently to get a nice glaze on things, but it takes some time.
How big is your fire basket? How many briq's or lump you start in the chimney also influences how hot it will get and how fast, I.E. the more lit the faster it gets to temp.
Also make sure your fire basket is off of the bottom of the barrel, if it isnt. Need about 2 inches.