There's a classic book from the early days of aviation that all pilots read: Fate is the Hunter
The author was on a final flight before a long-awaited fishing vacation. The plane was making awful noises. He finally crawled into a wing cavity to explore, telling his copilot to do nothing. He then ignored the issue, and flew cautiously to a safe landing. There was a welcoming party. The other two planes of his type, same service history, had crashed while he was airborne. A long investigation concluded that the only way to avoid crashing was to do nothing. He took this as an omen, and retired.
I believe that you're oversteering. Perhaps you're also starting with too much fire; always light just enough charcoal to pass command to the temp controller.
See how close to sealed you can close the upper damper without putting your fire out. Partially close the valve on the bellows, if necessary. Wait twenty minutes between reactions.
I like to file things into psychological categories. Controlling a fire, like some but not all cooking tasks, gets better when one stops "caring so much".
I tend to place my controller temperature probe through the top lid hole that normally holds the analog thermometer, with an alligator clip (roach clip) as stop. This can read cold at first, and hot later, but I've had better luck controlling fires this way than with the standard advice to position the probe an inch away from the meat. It eventually doesn't matter; for low & slow the entire cooker converges on the same temperature, after this initial imbalance.