what are some areas that vote for the same party as they did decades ago

[RINO Tom]

The list changes significantly if you MUST include "for different reasons."  A good example the OP gave was Shelby County, TN, which went from Solid South White Democratic (for the most part) to urban enclave with a strong minority vote for the Democrats.  However, the reasons for Kansas' Republicanism aren't that different from back during the Civil War, once you obviously account for certain issues (Unionism, slavery, etc.) not existing anymore.

[RINO Tom]

I've always wondered why Eastern Tennessee has been so heavily Republican even during the Solid South days. Carpetbaggers perhaps?

Hillbillies are not plantation slaveholders.

I think it goes beyond this, as plenty of hillbillies in the Deeper South were convinced that their economic well-being depended on a thriving South (and therefore thriving slave power).  That argument didn't work in places like Northern Alabama, Eastern Tennessee, etc., as their economies weren't tied to slavery, and they (rightfully) felt totally betrayed by their states choosing to go to war with their country for the slave power's interests.

[RINO Tom]

One thing I'd be curious about:

Do white people in these ancestrally Republican areas of Eastern Tennessee do things like put Confederate flags on their trucks or otherwise express enthusiasm for Muh Southern Heritage?

My guess?  As the Confederate flag has become more associated with being a proud cultural Southerner and less with the treason committed by some dead traitors who happened to be from the Southern states in a specific decade, there's probably been an uptick.