Asus AC66U Don't Want To Change Firmware On Router

I just got a new Asus AC66U. When I play games I have severe stuttering now using the 5Ghz band. I ran a ping to the router and every 20-30 seconds it jumps up from 1ms to 100-900 for 2-4 pings then backs down. I tried running ping test on two computers with the same result.I tried fixing the 5Ghz to a specific channel. I've tried upper channels, lower channels, I've adjusted the channel width from 20-80Mhz. I've changed the preamble from long to short, I've upped the transmit power, I've turned off PnP. I haven't been able to change a setting that made a difference.

I did notice that the lag spikes were much less frequent in the morning when I tested, before everyone was using the internet, although I saw an occasional ping spike. They must be related to router load.i don't want to change the firmware on the router in case I have to return it. I spoke with Newegg and they're going to send me a replacement router. I doubt that it's the hardware, but this will be a good way to know for certain that it's not the hardware. Once I get the new router I'll test everything again including trying the ping with a LAN cable.