NEW YORK--(BUSINESS WIRE)--As part of its ongoing surveillance, Fitch Ratings upgrades two and affirms three outstanding classes of the CarMax Auto Owner Trust 2013-4. A full list of rating actions follows at the end of this press release. KEY RATING DRIVERS The rating upgrades and affirmations are based on available credit enhancement and loss performance. The collateral pool continues to perform within Fitch's expectations. Based on the current structure and credit enhancement, the securities