Some information would help. what type of cooker, what grade of brisket, what kind of fuel, what kind of temperatures, what is your process for preparation... If you provide that information, the help you get will be much better.
Fell all to pieces certainly sounds like overdone, dry is a lot tougher as that could be either.
the meat thermometer was so far past the top reading, it read Taylor
"perhaps...but then again...maybe not..."