Got the hmi in today from dokus on eBay and installed it. Android auto works, maps, waze and phone calls in/out work. Google assistant doesn't hear me and I don't hear it, and I can't get sound from Google play music or maps directions but I can live with these (for now at least)
My truck's a 2015.5 with a build date of 6/2015. I did try just the updated USB plug first, no dice it needed the 2.5 hmi module. Also the radio module # is 13506455, attached a pic incase that wasn't the right number off of it. If I attempt the dealer firmware upgrade I'll post the progress but for now I'm content.
This thread is full of useful info, thanks to all!