On two occasions, Diffey covered both series on the same day. On 23 August 2015, he called the Belgian Grand Prix from NBC's base in Stamford, Connecticut, before he and Matchett traveled to Pocono Raceway for the ABC Supply 500. Likewise, on 3 September 2017, Diffey called the Italian Grand Prix in Connecticut and then traveled to Watkins Glen International for the IndyCar Grand Prix at The Glen. Diffey's open-wheel focus shifted solely to IndyCar in 2018 when the US Formula One television rights were transferred to ESPN.