James's father,
Ernest Duff, founded Southern Tire Mart in 1973. James and his brother Thomas both worked there as teenagers and assumed control of the struggling company in 1983. They later sold it in 1998 to Tire Distribution Systems. In 2003, they purchased the company back for $15 million and rebranded it as Southern Tire Mart. At the time of the purchase, sales revenue was $90 million. By 2025, Southern Tire Mart's revenues had grown to exceed $4 billion, making it the nation's largest truck tire dealer and retread manufacturer. James and Thomas co-founded Duff Capital Investors, a holding company with revenues of $6 billion. DCI is the largest privately owned business in Mississippi. Since 2009, the brothers have been the only members of the
Forbes 400 list from Mississippi. Together, they remain the wealthiest individuals in Mississippi. == Personal life ==