InstallHTC Sync Manager on your PC before proceeding ahead, by putting your phone into install mode.
Now once you have flashed the ruu or you are already on stock verizonrom and also installed htc sync manager, lets proceed ahead :
1. Download DFS Tool 2. Skip this step if you are using a CDMA SIM. Now put your phone into cdma mode by going into Settings>Mobile Data>Network Mode>LTE Only Mode.Also enable USBdebugging. 3. Open Phone Dialler type on the Dial Pad ##3424# and press call button. Phone Should eneter in diag mode. If you are on MM phone will ask for MSL code just enter 000000(6 zeroes). 4. connect your phone to the computer and install DFS Tool You just downloaded on your computer. 5. Once you install DFS then open it. 6. it will ask you to login…. My advice just click on the red cross on top right of login dialogue(That Is what i did).Still if you want to login go to cdmatool.com create id and use that id to login into dfs tool. 7. Now you will see your m8 listed as PORTXX(X – Refers to any number between 0-9) or something like that in DFS Tool. Just double click on it. 8.On the DFS Logs window you should read something like device connected. 9.Now in main DFS Window click on Band Tab.then under bands tab you will see two tabs, HSPA and LTE click on Latter one.. 10.Click On Read. 11. Select the LTE bands you need. 12. Click write 13. Restart Your Phone Once. 14 Put It Back Into GSM Mode/CDMA mode depending on your network provider.