Gary played his collegiate ball at Manhattan College, where he left as the school's career hits leader after the 2005 season. Diaz played for Team Connecticut for six seasons, including two National Championship teams and a National Runner Up. He was named the National Tournament MVP in 1997, and is TCB's only four time All American. Diaz also currently coaches in the TCB 18u program. He is an instructor at many of the Academy's hitting and fielding camps and clinics.