I also had major major issues getting temps to hold steady. It was either blazing and 400* or choke the fire, and billows of white smoke. BUT after a couple times using and experimenting, I found that if I build the fire all the way to the right of the firebox, instead of the middle or closer to the inlet to the smoke box, WAY easier to control. Night and day. It was pissing me off, watching all these videos of people just cracking/closing the butterfly damper and raising/dropping temps like it was nothing.
I use 9" splits, throw a new split on when i notice temps dropping and 10* or lower than desired.
Using this method, i rarely get temp swings, +/- 10* either way. And beautiful TBS.