Pulled BBQ Chicken

This was a redo for our family, which is a rare opportunity.
4-5 frozen boneless skinless chicken breasts
2 TBS Brown Sugar
1 1/2 TBS Worcestershire Sauce
1 12oz. Bottle BBQ- I like Jack Daniels #7

Turn on crock-pot and mix brown sugar, Worcestershire sauce and about 1/2 the bottle of BBQ sauce together. Add the chicken and pour the remainder of the BBQ sauce over the chicken.  Cook on low for 3-4 hours.  Turn chicken over- (if home) I usually then turn it up higher after about 5 hours of cooking time  and pull apart the chicken using two forks.  I then let it cook a little while longer then serve on buns.  You can cook it at a higher temp,but I put it in when I leave for work, so I use the lower setting to cook it all day.