While JimShoe is correct about lanes becoming exits, it's not a reason to go hundreds of miles out of your way. There are four areas where the two right lanes become exits... on the north side for those getting on the bypass (I-285), downtown for I-20, for the airport, and then again at I-285 on the south side. I go straight trough often and try and do it at mid day or at night staying in the third lane from the right. There are plenty of miles between these four areas to move over two lanes before you get to the next area.
Three months ago I was impressed with how little construction there was from AFTER where I-675 joins up with 75 (south side of ATL) to the Fla line.
*At Lake City Fl you might want to take 100 over to I-95 and then south. 95 through Palm Beach county moves very well, not so well in Broward/Ft Laud.
Another option is at Knoxville, take I-40 to Asheville (A OK interstate and better than ATL) and then I-26 to I-95 since you are going to Miami... about the same distance plus no tolls.