Here's what I found by using the OU website and past schedules:
Since 1999 vs SEC (including A&M and Mizzou), OU has lost in 1999 Independence Bowl to Ole Miss, the 2002 Cotton to Arkansas, 2003 lost to LSU in the BCS Sugar, in 2008 to Florida in the BCS Orange, 2010 to both Mizzou and A&M, and 2012 to A&M again. So, Big Game Bob is not undefeated against the SEC.