To anyone having trouble flashing the retail zips (haven't tried this with the OP's GPE versions), no you don't flash them in twrp or stock recovery for that matter.
THIS METHOD WILL ERASE ALL OF THE DATA FROM YOUR PHONE.
Make sure you have the drivers for this device installed.
You need mfastboot: http://goo.gl/w17Bxs
- Extract the mfastboot zip to a folder and open the retail zip you downloaded. Copy all of the files from the retail zip to the mfastboot folder. Open a cmd prompt on the mfastboot folder and "adb devices" to ensure your phone shows up and then "adb reboot bootloader". Once in bootloader issue the following commands:
mfastboot flash logo logo.bin
mfastboot flash boot boot.img
mfastboot flash recovery recovery.img
mfastboot flash system system.img
mfastboot flash modem NON-HLOS.bin
mfastboot flash fsg fsg.mbn
mfastboot erase cache
mfastboot erase userdata
Once your phone reboots you should have stock 4.4.4, no root. If you want to root, download a twrp .img and place in the mfastboot folder, issue recovery command (while in bootloader) replacing "recovery.img" with the "name of recovery file .img". Reboot and place current SuperSU.zip on sdcard and flash as usual.
I just went through doing all of this so I'd thought I'd type it out while it was fresh in my head for those that have no clue as how to go about this.
I repeat, I did this for the retail zips, not sure if the GPE updates will work in similar fashion.