You did not say what size brisket? A large (12lb) brisket can take 12- 15 hours or more to fully cook. Also what was the temp of the meat when you took it off the smoker and when it came out of the oven?
2 cups of mop sounds like alot. Was it warm when you added it? If not it may have caused the meat temp to go down when you poured it on. The more liquid you have the more heat it takes to get your brisket up to temp.
Some people are like Slinkys, they are good for nothing but can still bring a smile to your face when you push them down the stairs.
Down to one lonely ol' Bandera.