I've built a couple UDS's now and I'm having the same problem with both. When i first start out I have to light at minimum a chimney full of briquettes, sometimes even more just to get it up to around 250 degrees. I see others on forums and videos that only have to light around 10 briquettes to get it up to temperature. I have 3 3/4 intakes with 2 ball valves. I'm cooking a brisket as I write this and with a chimney and a half of lit coals on the top I have to have all intakes wide open to keep the temp up and it still seems to be slowly dropping. My basket on the one I'm cooking on now is 15 inches in diameter and a foot high wall made of 3/4" expanded metal. It's about 2 inches off the bottom of the ash catcher. I have had several good cooks on the UDS but seem to always have this issue in the beginning. Any advice would be greatly appreciated.