Help. Please. M7 ota update fail after guru reset. topic

Hi Guys.

I really need some help here and would really appreciate it as it's driving me up the wall for the past week. And I have combed through the forum looking for a solution before posting. So here goes.

I have a One M7 running on ARHD84 with 6.13.707.1 firmware. Learning of the coming OTA update for Lollipop, I decided to return to stock the best I can S-ON. Thus my nightmare begins.

1) I did a nandroid backup restore with a file named 2014-09-15--13-39-50 KTU84L release-keys (I don't have a nandroid backup of my own). It worked fine. Then I did the OTA update (6.13.707.4). It pops an error "Variant System Version".

2) Thinking it must be the nandroid issue, I went for guru reset 3.63.707.4 ROM and it installed with stock recovery and radio. Startup okay then I did the OTA update. It installed halfway and stopped to show a red exclamation error. I hard reset the phone and it went into a bootloop. It loops at the HTC logo. I went into fastboot, flashed twrp and got my phone back with the nandroid backup.
** Stock recovery goes into black screen.

3) Tried the nandroid again. Still Variant System Version.

4) Tried a lower guru reset 2.24.707.1 and it installed with stock recovery and radio. Startup okay and did the OTA update. It installed 1/3 and went into bootloop. This time it took me many many many tries to get back into bootloader.
** Stock recovery never happens, it just goes to black screen

5) Scoured the internet, came back a little wiser and tried the gurureset 3.63.707.4 again. This time I flashed the stock recovery again just to be sure. And this time, guess what.... same thing. Installs 1/3 and goes into the red exclamation mark. Only advancement was it did not go into bootloop.

My getvar

(bootloader) version: 0.5
(bootloader) version-bootloader: 1.57.0000
(bootloader) version-baseband: 4A.21.3263.04
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main: 6.13.707.1
(bootloader) version-misc: PVT SHIP S-ON
(bootloader) serialno: pewpewpew
(bootloader) imei: blablablablabla
(bootloader) meid: 00000000000000
(bootloader) product: m7_ul
(bootloader) platform: HBOOT-8064
(bootloader) modelid: PN0714000
(bootloader) cidnum: HTC__044
(bootloader) battery-status: good
(bootloader) battery-voltage: 3868mV
(bootloader) partition-layout: Generic
(bootloader) security: on
(bootloader) build-mode: SHIP
(bootloader) boot-mode: FASTBOOT
(bootloader) commitno-bootloader: dirty-6d8a0b9b
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0

Would really appreciate if someone could help me out here. At my wit's end.

Thanks!