I too am having the same issue on my Galaxy S3. If I put the phone in CDMA only mode, I get 3G. If I put it in lte/cdma, not only do I not get 4G, but I get no data connection whatsoever and the symbol doesn't show up (then i get this lte: emm error that you're getting but with a 7 at the end). It happened after I did the update to 4.3. I've spoken to 2 tier 1 techs and 1 advanced tech so far and have been unable to get it resolved. The advanced tech had me do a backup and reset and it actually started working momentarily. I thought the issue was resolved until I checked my phone like 5-10 minutes later and it was back to the same thing with the same error message. I've been trying to get this fixed for about a week now. I will let you know if I ever get it fixed.
Oh, and as far as the troubleshooting done with the 3 reps: updated prl, updated profile, reactivate device through settings menu, reactivated device through sprint zone, ##SCRTN# from PST screen. ##SCRTN from dialpad, force LTE from PST screen, and probably some other stuff that I can't remember right now.
I am currently having this error code too. I have done numerous updates and dialed ##72824# or whatever it is to hands free activation. This begun nearly a month ago and honestly I ready to can my sprint account and go else where if this can't be fixed asap.
You need to get sprint to send you the correct apn info for your phone to be able to get 4g and 3g the people at sprint are to stupid to realize that the problem is not with the ##78726# its with the apn they have on the update its not correct im having the same problem you have to ask the right people how to fix it sprint customer care dosnt know anything