internet speed is slow on nighthawk r7850 when wired

This is actually for the Nighthawk X6 AC3000 R7850 but is not included in the mandatory list I had to select to post this reply (smh...). I have the same exact problem. I have 450Mbs down from provider but more often than not, wired ethernet testing gives less than 200Mbs. If I connect directly to Spectrum modem, I get the 450 speed again. If I do a hard reset on the router, I get the 450 download speed again for a couple of days but then back to the slow 200 or less and the process repeats. I've tried changing a few settings but nothing works. I thought I did thorough research when selecting this modem but am now quite unhappy with my decision. My firmware for the R7850 is V1.0.5.68_10.1.75.