I am sure there will be opposition to this suggested route as the consensus seems to be that Atlanta is a piece of cake at certain times. Atlanta driving in an RV is tense and miserable regardless of time IMHO. I have heard all that before but here goes. We use this route every time for north south travel around Atlanta. 4 lane all the way. Virtually no traffic. Highway speed. Excellent road conditions. Few traffic lights. It really works. May be an hour longer to Orlando because its a more relaxing pace. You will not run into a traffic jam on this route. In fact there will be times you won't see a car for a bit of time.
Southbound out of of Chattanooga on I-75 exit 312 SW on to GA 53. Head to Rome and turn left onto GA 1 the Rome bypass. Go to US 411 and turn right and proceed to US 27. Take it south to LaGrange and turn left on to the Davis road bypass (this bypass new and it may not show on your GPS). Proceed to GA 109 (at the LaGrange mall) and turn left and proceed to I-85. Proceed north toward Atlanta about 1,000 feet on I-85 then exit immediately south on I-185 to Columbus. As you pass through Columbus you will approach the entrance to Ft Benning which you will recognize as a very ornate bridge. As you pass under that bridge exit right on to US 82/GA 520. Proceed to Tifton (using the Albany bypass) and return southbound to I-75.
Google maps says going straight through ATL from Cincinnati to Orlando is 13hrs 15 minutes 901 miles. (Assumes no traffic jams?)
This route we use is 951 miles and 14 hrs and 45 minutes- and you will not run into traffic in GA
We run this route consistently with our moho and toad. About 80% of it is 65 mph the remainder mostly 55 except in a few short urban areas. Its scenic, relaxing and an enjoyable ride compared to the Atlanta traffic, road surface and construction mess.