my 2 cents.
I am in Arizona but I use my Vzw M8 on a gsm hspa carrier only. i am on 4.4.4 with soff. I paid my 25.00 to get my phone soff as i couldnt find any other way. I wanted a GPE phone and strip anything vzw related. i have read verizon has different memory areas on this phone and is why you cannot flash a a gsm ruu on it.
first things first. soff fully unlocked (verizon does NOT sim lock these phones) Sunshine 25 bucks
you need a special vzw version of twrp 188.8.131.52 so it will flash roms correctly.
backup your phone !
i recomend if you want a pure android experience you use DigitalHigh Gpe for M8vzw rom
set your apns
i apologize for crappy typing. using my tablet
hope this helps someone. the right vzw version of twrp was my biggest issue.