RT-AC5300 unsatisfied with speed - eviltoast

Hey guys, I was hoping you had some insight for me. I just upgraded my internet to gigabit, and I have confirmed that I am getting gigabit speed when plugged directly in to the modem, but when connected to the router I only seem to be getting about 450mbit. Doesn’t seem to matter if it is wired, wireless, or even using the routers built in speed test in the QoC menu, I can’t get faster than 450mbit. I have a brand new cat6 cable between the modem and the router because I thought maybe my old cable had degraded or something, but have seen no change with the new patch cable. I did a factory reset on the router hoping that that would help, but no luck there either. Like I said, I did confirm by wiring a computer directly to the modem that I am getting gigabit speed to the modem, so it is very clear to me that it is something with the router. Any ideas or things I should try before replacing it?