I've built myself a UDS (because I could), and have done a couple of cooks now, with good results.
Initially I had a problem with getting up to/above smoking temperature (fixed with more holes and different charcoals), but my cooks are always longer that the internet says that they should be.
I am using electronic probes for meat and grill temp, along with two separate (top and side mounted) off the shelf thermometers.
I can maintain temperature really well (reading on both electronic and normal probes), but the cook is way too slow, normally taking longer than expected.
I have had a small (1.5kg) brisket on today, and it has been on for 8 hours already and looks like it will need another three or four!
My first cook was a chicken, which my neighbour swears only takes 3 hours in a WSM, took 6 hours in my UDS to come to internal temperature.
Could it be the heat circulation (though the probes next to meat read ok?) I have a pizza tray baffle, and a drip catcher bowl (no water) above the coals, and a rounded lid (from a weber).
Anybody had the same problem?