Some information located here:
https://texags.com/forums/46/topics/2930602I looked at the new 2018 STX pretty hard a few months ago, but I ended up buying a 2016 Lariat 502A for $6-7k more than where the STX prices were landing.
Granted, I was looking at 3.5L SuperCrew, 4x4, with the 6.5' bed, and the one I found was in Arizona... that's a long road trip home.
Features that you can't get with the XL, and are either cost-prohibitive or just difficult to add-on later include sliding rear window, sunroof, folding mirrors, and HD radio. Some of the other stuff can be added yourself for minimal effort or money.
The STX is a great option to get the center console and Sync3 system in a lower model truck.