Klassen joined the El Paso Diablos for the 1997 season. Playing in the AA–level Texas League, Klassen appeared in 133 games and his average rose to .331, which would prove to be a career–high. Klassen drove in 81 runs, also the most of his career, while hitting 14 home runs and stealing 16 bases. Klassen's best statistical season in the Brewers organization was also his last. On November 18, 1997, Klassen was selected by the Arizona Diamondbacks in an expansion draft.