Combine onion, garlic and Jack Daniels in a 3 quart saucepan.
Sauté until translucent, about 10 minutes.
Add all remaining ingredients and bring to a boil.
Simmer uncovered until reduced and thickened (about 15 to 25 minutes).
Add more Jack Daniels if a stronger flavor is desired.
In a large bowl combine chicken, oil, grill seasoning, salt, and pepper. Allow to sit at room temperature about 20 minutes.
Heat grill to high. Spray well with cooking spray.
Sear chicken on each side for 2 minutes.
Reduce heat to medium and continue cooking for about 25 minutes, turning every 3-4 minutes to crisp both sides.
Baste with barbecue sauce and continue cooking for 6-7 minutes, turning often and re-basting.