Slattery set a new best of 8:15.69 minutes at the 2007 Memorial Van Damme meeting (second fastest American that year) and was third in the steeplechase at the Prefontaine Classic. Despite this form, he failed to finish at the USA Outdoor Championships. As one of the fastest performers on the circuit, he was invited to the 2007 IAAF World Athletics Final in Stuttgart, where he finished eighth. He came second at the 2008 Reebok Grand Prix in New York City with a run of 8:28.21 minutes, but failed to finish at the Olympic Trials final. After a low-key 2009, he returned to form on the 2010 IAAF Diamond League circuit and came third at the 2010 USA Outdoor Nationals. In 2011 he ran a season's best of 8:28.52 minutes at the Shanghai Golden Grand Prix, but pulled out of the steeplechase heats at the national championships.