The hardware WPS button method of clearing nvram on the RT-AC66U works correctly up to version r26339. In later versions, the WPS method clears the 5GHz Wi-Fi radio to "2.4 GHz TurboQAM". This can be remedied by flashing r26339 on the unit and again clearing nvram before upgrading to a later release.

May 07, 2018 Features | Asuswrt-Merlin Jun 28, 2020 Download ASUS RT-AC66U AsusWrt-Merlin Firmware 380.70.0 The AsusWrt-Merlin firmware was developed with the primary goal of boosting the original ASUS firmware, fix bugs and also add new improvements. This package includes a customized firmware targeted at ASUS routers that brings various changes without … RT-AC66U | Networking | ASUS Global

Jun 28, 2020

May 24, 2017

May 07, 2018

Asuswrt-Merlin - Custom firmware for RT-AC66U