[Nexus 6 Q&A, Help & Troubleshooting] terrigan:
Sorry for cluttering up the ROM thread with my issue, I'll continue my research here. I need a little assistance and I do believe it's a CM12 and CM12.1 issue regarding LTE in my area. Here's a brief synopsis of the issue I have.

When I got my N6, i played around with stock 5.1 for awhile. I live in a rural area in Wisconsin where I get 2 bars of LTE from a Verizon tower on my Jetpack and I got it on my old S5. When I brought my N6 home however, regardless of what i tried in Cellular settings, i had nothing but 3G unless i switched to LTE/CMDA/UMTS mode where i would get my Data. I was unable to make or receive calls using this and I called Verizon. After a brief checking on their end, they turned on Enhanced LTE on my account, which made the toggle appear under Cellular which i flipped on. I was then able to make and receive calls and get LTE data.

My issue with both CM12 and CM12.1 is that the toggle for LTE/CDMA/UMTS doesn't exist on either build. If I flash the most currently nightly of CM12 or this Alpha, I am stuck with 3G at home. I have switched Cellular from LTE to Global on CM12 and it doesn't make a difference. The Carrier on the ROM usually reads 31000 rather than Verizon in the status bar. I have attempted to take the working APN from my stock rom and mastamoon graciously posted his apn-conf.xml on the ROM thread which i replaced mine with and still no LTE. Now here's the kicker. I drove into a different town that has a Verizon LTE tower and flashed the latest CM12 nightly from stock 5.1 and was greeted with LTE out of the box. This leads me to believe that there's something different about the LTE tower here by my home which requires this toggle on stock to even reach. It's a fairly strange issue, to be sure. I've flashed non-CM Optipop and flipped the toggle in the rom and have LTE here at home.

Now I know most people think, "Well that's your problem in your area, I don't have it so why make it a problem with CM12." Mainly because it's a technical issue which can be resolved by running stock 5.1 or a 5.1 ROM so there's some integral component in CM12 missing that stock has, perhaps tied to that toggle switch. My main goal for the N6 was to end up with CM12 and I really don't plan on giving up on it. I'd like it to work here at home though and as it stands, I can't use it if there's no LTE. (I tether and the 3g tower is crap) So there in a nutshell is the issue i'm having. I'd appreciate any advice to get this working on my phone.

Edit: Doing a bit of further research and comparing my phone to my friend's N6 that lives a town or two away, I've again flashed CM12 nightly dated 4/11. I was able to get LTE from the tower by my house by switching to Global and setting US Radios in the hidden menu. I could not make or receive calls however. The Enhanced LTE toggle does not exist under the Mobile menu and the VoLTE Provisioned flag toggle does not exist in the hidden menu. (#*#*4636*#*#) This was required to be on (even on stock 5.1) to make calls.

Edit: Ok so hmmmm.... I fiddled around some more, tried a different 12.1 rom and went back to this unofficial and now for some unexplainable reason it all works. I really wish I knew why. The only caveat is that VoLTE doesn't work.. possibly because it's a 5.0 rom and not a 5.1? My data drops out when the phone rings on LTE.