Some of the early Job 1 2017 trucks did not receive the updated connecting rod design that most of the later 2017 trucks received and all 2018 and 2019 trucks have. The heads changed somehow in the 2018 trucks but the part number didn't change for the heads but the casting numbers did so that would signify some kind of possible change, I don't think it will affect any performance though. The picture below does a good job showing the major changes from 2017 to 2018.
Big one was The Limited Trim Super Duty was introduced for 2018.
From 2018 to 2019, the biggest change I know of is the change from Sony sound system to Bang & Olufsen sound system brand, and some new color options I believe. I don't think much else changed.
I'm hearing a lot of talk about the possibility of a 10-speed trans option for 2020. That's just hearsay right now though. It wouldn't surprise me though becaue the F150's and mustangs have 10-speed trans options already. So do some Chevy/GM trucks.