Why your chicken keeps drying out
It is almost never the recipe. It is the lid, the vents, and a thermometer you have stopped trusting.
Check the thermometer first
Put it in boiling water. It should read 100 °C, give or take one. Most cheap probes drift by five or six degrees within a year, always in the same direction: reading high. You pull the bird at what you think is 74 °C and it passed 80 twenty minutes ago.
Then check where you are measuring
The thickest part of the thigh, not touching bone. Breast and thigh finish at different temperatures — 65 °C and 75 °C — and a whole bird cooked to one number will always disappoint on the other. Spatchcock it and the problem mostly disappears, because everything sits at the same height above the fire.
And stop opening the lid
Every look costs you five minutes and a swing in temperature. If the lid is on and the vents are set, the fire is doing something stable. Opening it is how you turn a stable fire into a guessing game, and the guessing is what dries the bird out.