How can I use my own router without losing speed?

[Athomas3]

I have a fios gateway router for gigabit internet, but not only does the lan port on it for whatever reason only give me 500/500 speeds, the wifi is incredibly weak. I wanted to use my nighthawk router instead of it but I think I keep doing it wrong. So my current set up is the gateway router’s wifi signal is off, and I put the nighthawk (AC 1750) into AP mode and connected it to a Lan Port on the gateway. When I tried to use just the nighthawk, I unplugged the gateway router, turned off AP mode on the nighthawk, and plugged the ethernet straight into the nighthawk WAN. It was working but only had 100/100 wifi speeds on the 5ghz line at best, while standing 5 ft from the router. Did I do something wrong?

[jonjones1]

https://www.wikihow.com/Use-Your-Own-Router-With-Verizon-FiOS

and 

https://kb.netgear.com/23977/Will-my-NETGEAR-router-work-with-Verizon-FiOS