[One (M8) Android Development] gmsteve455:
Hi and thanks for your thorough post. Here are answers to your questions in Red:

My M8 is a former GPE purchased from Google

What do you mean exactly by"former GPE"? Is it still running stock GPE software/firmware, or was it "converted" to something else by RUU, or running custom ROM etc.? In addition, it's best if you do fastboot getvar all, and post the results (delete IMEI and serial number before posting) so we can see exact info about the current state of the phone. Also, if it says the bootloader is LOCKED, UNLOCKED or RELOCKED near the top of the bootloader screen.

The M8 was originally a GPE, not converted from sense. I shortly after switched over to Cyanogenmod, now Lineage. Unlocked Bootloader,

S-off, rooted. I'll post the getvar all below

so I'm assuming I'd be in the unlocked/developer build section. It looks like the latest is 12.03.2015.

That would be an incorrect assumption. Google Play Edition (GPE) is different from Developer's Edition (basically US version of unbranded Sense), for which that RUU is specifically intended for. Depending on the info you provide, you might be able to use that RUU If you want. But again, it depend on what the state of your phone is, and what your specific goal is. But it is not the RUU for the GPE version (it was never officially posted by HTC to my knowledge).

Understood

My baseband version is 1.23.21331149.A4198.01_F. Anyone know what is contained in the 12.03.2015 download from HTC?

I think that is a really old radio baseband number. Unless the GPE numbers vary drastically from the Sense ones (there are some differences in the conventions, like the firmware numbers) that would be a Kitkat radio, which makes it very old (2-3 years) versus what the "final" radio versions made available by HTC (Marshmallow).

Understood, would like to know what I should download and flash for the updated radio.

If I were to download this, would i just do a nandroid backup, load thier firmware and then restore from my backup?

Depending on the state of your phone, and what your goal is, it's either not that easy (more steps involved) or easier than what you propose. You need to provide the info requested above, before we can answer that or direct you further. Also, what is your goal? Do you want to run custom ROMs, but with updated firmware? Or do you want stock GPE? Or stock Sense? Do you want root?

My goal is to just update to the latest available radio and other firmware keeping Lineage OS and root intact.

I Will post the getvar info in the next post.

As a side, the phone is working pretty well. I'm not convinced that the reception is the best which is why I'm seeking the latest radio. As I stated, I'm running Lineage OS 14.1 and have been using the Pixel launcher and wallpapers. It's pretty nice and snappy. Battery life is decent but could also be because I replaced the battery about 8 months ago when the charging port crapped out on me and I was already in the phone replacing that.

Thanks again for all of your help.

Steve

---------- Post added at 01:41 AM ---------- Previous post was at 01:30 AM ----------

Here is the dump of the fastboot getvar all:

(bootloader) version: 0.5

(bootloader) version-bootloader: 3.19.0.0000

(bootloader) version-baseband: 1.23.213311491.A13G

(bootloader) version-cpld: None

(bootloader) version-microp: None

(bootloader) version-main: 5.07.1700.15

(bootloader) version-misc: PVT SHIP S-OFF

(bootloader) serialno: ************

(bootloader) imei: ***************

(bootloader) imei2: Not Support

(bootloader) meid: 00000000000000

(bootloader) product: m8_ul_ca

(bootloader) platform: hTCBmsm8974

(bootloader) modelid: 0P6B17000

(bootloader) cidnum: GOOGL001

(bootloader) battery-status: good

(bootloader) battery-voltage: 0mV

(bootloader) partition-layout: Generic

(bootloader) security: off

(bootloader) build-mode: SHIP

(bootloader) boot-mode: FASTBOOT

(bootloader) commitno-bootloader: 11459804

(bootloader) hbootpreupdate: 11

(bootloader) gencheckpt: 0

Thanks again, let me know where I can download a radio appropriate for my device.

Steve