New 400Mbps internet, 300+ Mbps on wireless but only ~165 Mbps on wired

A bit of a long story, but we recently got 400Mbps from spectrum hooked up at home. Running a speedtest from ookla's tool I'm hitting around 150Mbps on ethernet. At first I thought the service was just not as advertised and the speeds wouldn't be any good... Weeellll a different guy came to audit the first guy's work, and after working out a couple issues he found, he did a wired test from our router and was hitting over 450Mbps. He told me to run a test from my computer and I was disappointed to see my speed was still around the 150Mbps mark. He said I might have a bad NIC or a 10/100 card which confused me because it didn't seem like I'd be seeing speeds as high as I do if that were true. So I said "whatever, it's probably throttled and his tool is designed to show bs results" uuuntillll I ran a test on wireless from my phone and hit over 300Mbps... So now I'm upset that my phone on wireless is hitting much higher speeds than my gaming PC on wired. Any help would be greatly appreciated, I've done as much googling as I can but there are just so many people with problems with being stuck at 100Mbps and using incorrect cables or incorrect hardware that I can't find anyone with a similar problem.

NIC: Realtek PCIe GbE Family Controller

Router: DLINK DIR860L

I double checked, and the on-board NIC is a 10/100/1000 and it shows it's running in full duplex at 1 Gbps in the connection information...
I'm using a Cat6 cable (and tried with a 5e cable I know for a fact is good just for good measure)
I have the most recent drivers freshly installed directly from the manufacturer page. Driver date is showing it's only around 3 months old.
I've tried power cycling, unplugging my PC overnight, disabling "green ethernet" and "energy efficient ethernet" in my adapter options.
The only thing I could find listed regarding my router's ports is that it's advertised as "gigabit ethernet" so I don't think it's a 100Mb port on the router. And just to double check I tried connecting directly to the modem and was getting identical results.
All the QoS options I could find on my adapter and my router configuration have been disabled


I may end up purchasing a new network card, but I really have a feeling this could be fixed without resorting to that, so I appreciate any help you can offer.