I just
documented my steps of resolving a few unrooted, stock ATT ML2 phones
here
Don't understand how the NE3 would make a stock ATT ML2 go from 4.3 to 4.2 (as posted..)
(my step 1 was using ATT update over wifi if available.... however, in my case multiple phones FIND the ATT NE3 update 444 mb file but FAIL after reboot when update reaches 29 percent, no explanation given.)
2. Download from the link above (ATT Stock Firmware Thread) the Android 4.4 ( I537UCUCNE3 (4.4.2) ) 444 MB file,
3. Rename the 444 MB file to update.zip
4. Set SG4A phone into Developer Mode and enable USB debugging
5. Move the update.zip to a microSD card and insert into phone
6. Hold down simultaneously Volume Down, Power and Home Button and wait for Stock recovery/Downloading menu to appear
7. Select update.zip and let phone update ML2 to NE3