Does your computer have USB 2.0 or is it the older USB 1.1? If the latter, that's probably why it's taking so long. Also, make sure your battery is fully charged. If it loses power while doing the update, it will break communication, which will brick the update. Regarding the first phone, which you said did complete the update, make sure to do a HARD RESET immediately. It cleans up stuff that might be in cache and resets it to factory fresh, albeit to the ROM you're using.
You want to flash to CF03 at the very least, as that was the first official VZW ROM which supported the unlocked GPS. I think CC20 was a beta version that made it into the wild, but am not for sure. Also, you don't indicate whether you were trying to flash FROM a custom ROM to DF14. I would recommend trying to reflash the official base ROM first so that you're going from official to official.
I had trouble updating the ROM on two i910. I used the official DF14 upgrade software downloaded from Samsung. It stopped at 60% for hours and the battery was dead. I had to close the software and replaced the battery. When I connected it again, it entered emergency upgrade mode. Each time it stopped at a different %. After I tried many times, it went through finally.
I tried another phone. It had the same problem, but I didn't have the luck this time. I tried many times and it never succeeded. Then I tried to use UMDL. I couldn't manage to burn the dc22 ROM. It seems I had a better chance with CC20. The Switching USB to Phone step always failed. The phone may or may not be functional when this step failed. GPS seems not working with CC20.
I don't know what's wrong with the upgrade. I'm pretty sure I set up the phone and ActiveSync correctly before burning the ROM.