Need help with random reboot topic

I have a c6606 but I flashed the stock c6603 software that's 4.4.4 because T-Mobile didn't update past 4.3 but since I've flashed the c6603 software when I'm on the phone it will randomly reboot. I didn't wipe data when I flashed and I checked to exclude baseband flashing could this be the problem? Also my T-Mobile mobile hotspot was removed and I can't get into mobile hotspot without downloading a third party app there is no seeing for it in my phone should I reflash or something can anybody give a little advice