United Auto Group ( UAG) said operating chief Samuel X. DiFeo is retiring to assist with international operations. The Bloomfield Hills, Mich., auto seller named Robert H. Kurnick Jr. vice chairman. He was previously executive vice president. "Sam DiFeo has played an instrumental role in the growth of United Auto," said CEO Roger Penske. "We thank Sam for his years of service and are pleased to receive his continuing support and efforts."