Nexstar Financial Corp. will soon be working with Morgan Stanley Dean Witter Credit Corp., the residential lending unit of one of the nation’s largest retail brokerages, to provide private-label mortgage processing services. “After making the strategic decision to outsource our mortgage processing, we evaluated several service providers,” said Thomas White, president and chief executive officer of Morgan Stanley Dean Witter Credit Corp. “We came to the conclusion that Nexstar’s process efficiency and customer service experience…