I would like to go directly from my modem (Spectrum) to the Archer AX1500, then use a cat 5/6 wire to the main router in the house.     When I have the main router connected directly to the modem, my speed tests at ~450 MBPS.   When I connect the AX1500 to the modem and the main router to the AX1500 via wired connection, my speed drops to 95 MBPS.   This suggests it's acting like a FAST connection rather than a GIGABITE ethernet connection.   

Is there a setting or other change I can make to include the AX1500 in the stream without taking my rates down by ~5X?.

I'm adding this router so I can include a UPS for the modem, a router (the 1500) and a wifi based sensor that will text when it detects a relay opening.

Thanks,

Paul