I'll do one better....
1997 - W, Missouri, 31-10
1990 - W, Texas Tech, 17-10
1989 - W, Okie State, 37-13
1986 - W, Colorado, 13-10
1986 - W, TAM (Cotton), 28-12
1985 - W, Colorado, 36-13
1983 - W, Oklahoma, 24-14
1982 - W, Baylor, 21-14
1978 - W, Baylor, 34-28
14 straight over the Big12...