OK, I'll finally post it
Guys, everyone has been pming me for this, figure I'd make it public.
To enable TMOBILE 1700 AWS LTE on an Sprint Phone.
On a SPH-L720 you first need to flash the M919 modem.bin and NON-HLOS.bin. Then, replace the SPH-L720 files libril.so,libril-qcril-hook-oem.so,libril-qc-qmi-1.so with the Tmobile M919 ones.
Once you have done that and rebooted, you can actually go into the Debug Menu and select AWS 1700 for LTE and LTE/WCDMA/GSM for selection.
Use adb shel, su -, am broadcast -a android.provider.Telephony.SECRET_CODE -d android_secret_code://27663368378 to get into debug menu.
Once that is done, enable Modem Mode by executing
am broadcast -a android.provider.Telephony.SECRET_CODE -d android_secret_code://0808
and set to rmnet , dm, modem, fire up DFS, add port, spc unlock with your msl (get using MSLUtility.apk - must have wifi on). Final step in DFS, Go to Band Tab, select Nam1, select the little radio button RF BC COnfig in the lower right, click read to see your bands. Checkbox the WCDMA IV (AWS 1700) USA and click the write button. Repeat for Nam2.