If you are using I-75 South, the only real hilly part is just as you get into Tennessee, you have a pretty good climb. Once over that, no problems.
We came that route in July of this year and found a bunch of construction on I-75 in the south part of Kentucky. I am sure they are still working on it. A few lane closures, etc. Just be on the lookout.
On our route from Chattanooga to Columbia, I suggest you take I-75 South all the way to I-20 East, forgoing a trip around I-285 in Atlanta.
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