I will add to what I said about I-40 through the Smokies; Maximum grades are 6% and none of the pulls is longer than 5 miles.
I-85 to Atlanta is not very scenic and is (for me) scary once you get to Atlanta. I think the I-40 route is much more scenic and enjoyable. I have driven both numerous times.
One word of caution is to check NCDOT for travel conditions on the day you plan to do the drive. Every once in awhile an accident or rock slide will close down the highway for hours or even days.
Have a nice trip.
Upstate South Carolina
2000 Holiday Rambler Endeavor
2012 Honda CRV