went to https://www.ford.com/support/software-updates
entered vin, they said there was a software update
downloaded it and copied it to a USB,
truck seemed to recognize it then said "Sync Hardware is incompatible with this software update"
SAY WHAT ??
2018 F150, Sync 3, version 3.0, build 17276_PRODUCT

 

I would likely clean the flash drive, then redownload it.

 

Is it because the Ford site most current version is what you already have?

Go to Cyan Labs.
You can get most recent 3.4.

I just did it on my '16. Went from version 1.0 right to 3.4.

 

That "hardware incompatible" error usually means the update package from Ford's site targets a newer APIM revision than what's in your 2018. The Ford site sometimes serves the wrong package based on VIN lookups that don't account for mid-year hardware changes. Cyan Labs is the right call -- grab the latest 3.4 build from there. Make sure you format the USB as FAT32 (not exFAT), put it in the front USB port, and let it sit for a few minutes after the progress bar finishes before touching anything. The 3.0 to 3.4 jump is completely safe on your hardware.