I have downloaded the file three times now, on two separate windows PCs (one 8.1, one 7.) I have tried using Windows File Extraction and also 7-zip to unzip the downloaded files. I am following the directions in the README file, and unzipping part one to the root of a freshly formatted (ExFAT) USB drive each time. I have used three different USB drives (128gb USB 3.0, 64GB USB 3.0, 8GB USB 2.0.) I have tried using both USB ports in my center console and gotten the same result every time: The updating message displays at the top of my SYNC3 display, but never changes or goes away with no success or failure message of any kind before or after removing the USB drive. I have tried with the USB drive inserted before starting my car, and tried with starting the car first and then inserting the USB drive. I have always waited 25 minutes or more, and have waited up to an hour (always with the car running.) I have tried doing a "factory reset" from within the SYNC3 menus, and tried using the button combination to reset the head unit as well.
I have a 2016 fist without navigation.
I have the exact setup as you, and mine is working fine, so I'd like to help as well if I can. I'll tell you what I did step by step and see if it differs from you in any way. Mine was done on a Windows 10 laptop.
1. Downloaded file to My Documents
2. Right clicked on part one, then I chose "Open"
3. It brought me to two items, a folder and a file. Can't remember what they said.
4. Choose "extract all", then "browse", then whatever drive your USB is in.
5. After it's finished, start car, insert USB, wait 20 minutes until you get the "finished updating" message
6. Turn car off, take USB, then delete everything on it
7. Repeat for step 2
8. Wait 5 minutes after turning off car, restart, wait 1 minute to fully boot up, check version in the "About" in the "settings"
I hope this helps a little, as beyond that, I'm stumped.