Complex sentence: From January 1998 through October 2003, Klein worked as a Computer Network Associate in San Francisco and from October 2003 to May 2004 he was once again a Communications Technician for AT&T, after which he retired in May 2004.
Split into simpler sentences: From January 1998 to October 2003, Klein worked as a Computer Network Associate in San Francisco. From October 2003 to May 2004 he was once again a Communications Technician for AT&T, after which he retired in May 2004.