Well if anyone hasnt figured it out, I had so many issues getting help on this everyone had different methods, I tried em and I kept getting blocked from tethering on my plan, but I finally figured out a method that works for me and I havent went back since. I made a back-up of the Rom I started with, just in case I couldnt make it work after I flash another Rom because I dont like stock Roms.
1a. Select Rom of your choice, if your not already on it, if so (IMPORTANT) Factory Reset, & wipe all caches.
1b. If choosing a custom a custom Rom, make sure you Factory Reset, wipe both/all caches, and WIPE SYSTEM. Make sure rom is on your sd card.
2. Reboot and let phone settle, it should restore all apps after you sign in and set up.
3. DO NOT TOUCH your stock tethering.....PERIOD!!!!!!
4. Go to your settings to change/create APN
5. Create name of APN of your choice, mine is F@&kTmobile, Lol
6. Use fast.t-mobile.com in second setting under your name of APN.
7. Change both protocols to IPV4, and your set.
8. Select that APN and reboot immediately.
9. After reboot go to Playstore and purchase FoxFi and Wifi Tether
Router. Why I got both is because I run 3on3( PS3, PS4, Tv on 1 app)
Phones, Tablet, and Pc on the other.
10. Go to either app you decide to use and set it up properly, Wifi-disable scan, Foxfi-download PDA NET, might not need it, I dont.
11. Activate and tether your heart out.
The first time I did this it used some of my plan then suddenly stopped so dont jump off the cliff if you see your plan tethering being used.
Sent from my SM-N900T using XDA Premium 4 mobile app