Check out how strongly Republican Mississippi was for Nixon in 1972. I think that offers a clue that enough whites had gotten into the habit of voting Republican in presidential elections. Perhaps, while they identified with Carter, they had mistrust of Fritz Mondale as a Northern Liberal.
http://members.cox.net/rbt48/weather/Presidential_Elections/Mississippi_pv.pdf I think Carter got a boost with Mississippi whites when, just before election day, it came out in the press that Carter's Baptist church in Plains, GA, did not allow blacks to become members (perhaps even attend).
As for Virginia, Ford only carried it by 22,000 votes (a 1.33% margin). Enough southern whites identified with Carter to make the state much closer than it had been from 1952 to 2004 (excepting 1964).
Interestingly, if 7500 Carter votes in Mississippi had switched to Ford, Carter would have lost the state. That would have forced a recount in Ohio, which Carter carried by around 11,000 votes. Had Ohio also gone the other way, Ford would have been elected with a popular vote deficit of over 1.6 million.
