What recovery and version are you using? Did you try to download the stock ROM again, or check MD5 to make sure the file wasn't corrupted during download.
Did you try a Sense based custom ROM, there are several based on either the AT&T or "international" stock ROM, that are very close to stock, just debloated and with some optimizations (which are both good things). Personally, I'd recommend the international base over the stock AT&T ROM, anyway.
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Phone: AT&T HTC One (M8)
Tablet: Samsung Galaxy Tab Pro 8.4 (WiFi only)