Marc, I live in Knoxville and, on the off chance that you haven’t already taken your vacation, I can offer some recommendations regarding Memphis and Nashville.
I think you’re doing right by choosing to visit Graceland. I can also recommend a visit to Biel Street. If you enjoy a good baseball game, there is also a minor league stadium downtown where a fun evening can be had. I’m not a fan of baseball myself, but I do enjoy getting outside in the summer and autumn, and I am a fan of nachos with cheese.
Perhaps a visit to Shiloh battlefield while you’re in Western Tennessee? And Memphis must have some good historical attractions linked to the Mississippi River and its history.
Nashville is very fun. I wouldn’t say that I’m a fan of country music, but I found the Country Music Hall of Fame to be a very enjoyable museum. You may also want to stop by the Gaylord Hotel, which is a resort hotel with several nice restaurants. It’s a terrific site to see. Be sure to visit the Grand Ole Opry for a tour at least.