Complex sentence: Commerce has the third largest enrollment in the Texas A&M system behind Texas A&M University in College Station, Texas and Tarleton State University in Stephenville, Texas have higher enrollments.
Split into simpler sentences: Commerce has the third largest enrollment in the Texas A&M system. Only the main campus of Texas A&M University in College Station, Texas and Tarleton State University in Stephenville, Texas have higher enrollments.