How much did you have the vents open, and did you pre-heat the smoker to 255 before you put the meat in?
I have a buddy who did that, turns out he was trying to get the dome temp to 250 or whatever, dumping nothing but lit coals into the WSM with all the vents wide open. He was burning up his fuel before the smoker even got up to temperature.
The way I do it:
- Fill your charcoal ring with unlit briquettes
- Set your wood chunks around the edges of the ring
- Make a little hollow in the top of the unlit
- Fire up 10-15 briquettes
- When they start to ash over, dump them in the hollow in the unlit
- Assemble WSM, put meat on the racks
- Vents go wide open until grate temp is 200, then close down the bottom vents to around 1/4 open. Adjust until I get the temperatures set.