Big 4 firms recruit more heavily from schools with a good program and that has a history of turning out good candidates in previous years
GPA is not the be all end all for the Big 4 - They look at your internships, speaking ability, presentation skills, associations, grades, and work history.
To be an auditor and deal with clients you can not be introverted and many of the higher GPA students do not have the background to be a successful auditor. Those bookworms who constantly studied and did not intern, join associations, have extra curricular activities, or have previous work history were turned away pretty rapidly. 30-minute interviews with these folks felt like hours.
Good luck!