If you go through Alabama, traffic around Birmingham will begin to get bad around 2pm, taking you an hour or more to go south. Too many cars and too little roadway.
I work in Montgomery. If you are planning on staying the night in Montgomery, stop in Prattville (just north of Montgomery) and spend the night.
There's hotels in Marianna, Florida and we usually stop and spend the night at the Comfort Inn & Suites in Midway, Fl (just west of Tallahassee.)
Also, traffic in Nashville is bad during rush hour.
I've been able to successfully bypass Atlanta by making a big circle around to the west. I would get off I-75 in Calhoun, and head west toward Rome. Then south on 27 and then to Alternate 27 to Newnan. From Newnan, you can take the back roads southeast to get back to I-75 well south of Atlanta.