I have an RT-AC68U (technically a TM-AC1900 that I flashed to Merlin) and just upgraded my internet to a gigabit connection. The fastest speed I can get on a wired connection through the router is 250-300 Mbps. The problem is that I cannot enable NAT Acceleration. When I try to set the option to Auto, the router reboots but NAT Acceleration stays disabled. I am using firmware 380.70. I will say that I tried fully resetting all settings and this fixed the problem, but when I restored my settings back, the problem came back. Anyone have any idea what to do?