I do not remember the details anymore, but I did managed to find a file somewhere in XDA forums to work with Android 4.4.2 (at least that's what I wrote down). I just tried with an AT&T S5 (rooted) and tether works fine. Tried Speedtest.net and it gave me 3-4Mbps download speed.
Here are the instructions I saved. I did not write it. These instructions are correct as it works for my phone:
I got it to work after some tinkering. Instructions:
1) Mount /system RW (I use ES File explorer)
2) Navigate to /system/app
3) Rename a total of 4 files by adding ".bak" to the end of the filename-
4) Paste new TetheringProvision.apk into the /system/app directory (I cant remember
whether I used the one from this thread or another, so I attached the one I used below)
5) Reboot phone. During the reboot I got the "Android is upgrading" popup with a little
6) The first time you turn tethering on, you need to do it by going through Settings
--> More Networks --> Tethering and Protable Hotspot --> Turn on Mobile Hotspot.
It will give you the "Please wait while verifying" and then tell you to call AT&T
to get tethering added to your plan, but just hit the OK button, and a few seconds
later tethering should start. After this, turn it back off and now use the "mobile
hotspot" app and you can configure network settings like wifi network name and password.
I was able to resolve the "unfortunately settings stopped" error by correcting the
permissions on the new TetheringProvision.apk to match the old one, rw-r-r, then I rebooted and was good to go.