Complex sentence: As the 1990s began, BYU's football program's dominance began to lessen, although from 1989 to 1996, BYU won at least a share of the WAC Conference Championship every year but one (1994 in which Utah ended the season in the top 10).
Split into simpler sentences: As the 1990s began, BYU's football program's success began to lessen. Although, from 1989 to 1996, BYU won at least a share of the WAC Conference Championship every year but one (1994 in which Utah ended the season in the top 10).