Thanks for providing the links on your route, It sure is easier to think of nearby food with the roads in mind. You did leave off the I-40&75 connection in Eastern TN from where I-81 ends To Chattanooga. That is important for a snack-stop at the Mayfield Dairy
Just off I-75 at exit 52 (Athens,TN) about 5 miles off the freeway on the east side . Mayfields makes some of the best regular (as opposed to soft-serve) ice cream we have ever enjoyed. It is a big dairy operation with a nice visitor's center/ ice cream parlor. Makes a great break from a long stretch of Interstate Driving.
On your return trip, If you want a really great BBQ experience about 2 hours out of Memphis, Get off I-40 at Lexington TN and check-out the Hays Smokehouse
. There is a whole series of raving reviews on a thread on this site called TN BBQ. A bunch of us went there in Feb and were very favorably impressed. The timing may be wrong on your schedule to do this, but if it is a thurs-fri- saturday, I would suggest that you really consider it. Whole Hog BBQ is not common in your part of the world, and is a great thing to watch and eat.
When you come up to Louisville, depending again on your timing for meals. Head east towards Lexington on I-64. Get off at exit 28 (Simpsonville) and follow the signs to the Claudia Sanders Dinner House
on U S Hiway 60. Check the review on this site for the place but I give it a super recommendation for a family lunch or dinner in a really "Bluegrass Horse Country" atmosphere. Chicken is the specialty and it is quite good, but the star of the show is/are the family style veggies. Southern Style Tomatoes, Mock Oysters (EggPlant), Corn Pudding,and A great Creamed Spinach are delivered to your table ..not one of them, but all 8 veggie side dishes. We also like the Chicken Livers. This is NOT a roadside hash-house, but the prices are reasonable for sure. You can then take one of the state roads up to I-71 to get back on course without backtracking to Louisville.
I'll add some more after considering the I-59 rt a bit. But these will defineitly keep you happy.
ADD- Just off I-59 at exit 153 in Meridian,MS is Montana's BBQ/Seafood Buffet
. Inexpensive, and pretty good too. We have visited the one in Pensecola several times. Here's a link to their Web-site for Map and Menu.. http://montanas.com/meridian.htm