I don't think you need to cook an 11lb brisket 12 hours. That's probably why it's dry. I normally get mine off the heat when the IT reaches 180. 190s are fine too, but at that point, they just need to be wrapped up well and kept warm. I rest them with the temp in the 180-190 range for 3 hours or so, then it's ready. Staying in he pit with temps as described for that amount if time above the target temp probably is what went wrong.
Custom 30"X84" competition-style RF trailer smoker
Pecos 20"X60" OS by Old Country BBQ
Char Griller 5050 with side box
Baby Arm BBQ