Autotrader, a Cox Automotive brand and America’s online leader for car buyers, and EchoPark Automotive, one of the nation’s top sellers of pre-owned vehicles, are partnering with Dover Motor Speedway on The Monster Mile’s signature event of 2025.   The Autotrader EchoPark Automotive 400 on Sunday, July 20 (2 p.m., TNT, Performance Racing Network) is the centerpiece of Dover Motor …