Trying to unbrick my AT&T HTC One topic

Hello all, I've been using these forums for information frequently, but this is the first time I've run into trouble. I updated my AT&T HTC One to the GPE, but decided I wanted to go back to stock with the impending HTC Sense 5.5 update around the corner. I had gotten GPE via rumrunner and the methods at htc-one.wonderhowto.com (I can't post the direct link).

I had then reverted back to a rooted stock ROM, but it would not perform OTA updates. So, my next step was to get S-ON and re-lock the device. I accomplished those, but somehow I now have no OS - I can get into recovery (stock), but cannot perform anything from there. Factory resets and wipes do nothing for me. I have access to fastboot, and have attempted running various RUUs but all of them give me error code 155, which appears to be due to the wrong version. However, I have tried all of the AT&T US RUUs I can find, so I'm sort of at a loss there.

I thought maybe I could get unlocked again so that I could load TWRP again, but running the HTCDev unlocktoken command does nothing, other than tell me it was successful - it stays on the fastboot screen instead of showing the option to choose Yes/No to unlock.

So, after hours of attempts, I'm sort of stuck. Could anyone help point me in the right direction? By the way, my device reads TAMPERED and RELOCKED in the bootloader, and S-ON. Below is the output of my getvar all:

(bootloader) version: 0.5
(bootloader) version-bootloader: 1.56.0000
(bootloader) version-baseband: 4A.22.3263.14
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main: 4.06.1540.2
(bootloader) version-misc: PVT SHIP S-ON
(bootloader) serialno: HT35YW900577
(bootloader) imei: 354439055719951
(bootloader) meid: 00000000000000
(bootloader) product: m7_ul
(bootloader) platform: HBOOT-8064
(bootloader) modelid: PN0712000
(bootloader) cidnum: CWS__001
(bootloader) battery-status: good
(bootloader) battery-voltage: 4325mV
(bootloader) partition-layout: Generic
(bootloader) security: on
(bootloader) build-mode: SHIP
(bootloader) boot-mode: FASTBOOT
(bootloader) commitno-bootloader: dirty-bee46337
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0
all: Done!
finished. total time: 0.040s