Diagnose the result, change one variable and keep public safety guidance separate from texture adjustments.
Choose the closest result
Use these fixes after a first attempt, then change only one variable at a time so you can tell what improved the next batch.
Dry or stringy
Pound thick breasts to an even thickness, start checking 2 minutes earlier, and rest before slicing. If it still dries out, lower the next cook by 10-15°F.
Pale outside
Pat the surface completely dry, use a light oil coat, and avoid wet marinades until the final minutes so the breast browns instead of steaming.
Cold or underdone center
The piece is likely too thick or crowded. Split very large breasts, leave airflow around each piece, and verify 165°F at the thickest part.
Tough edges, soft center
The thin end is overcooking before the thick end finishes. Even out the thickness or tuck the thin end under before cooking.
If the center may be undercooked, keep cooking in short intervals and verify the safe internal temperature with a food thermometer. Texture advice never replaces a safety check.