ASUS B550-F gaming ROG Strix LAN Problems

I am supposed to have 900mbs but when I run a speed test it will get maybe 300 if I am lucky and then bottom out to 0. I am still connected to the internet but will have huge spikes of lag where a webpage will take forever to load. I have tried swapping LAN cables with my boyfriend's computer and he will get 900mbs on my cable but on my computer with his LAN cable I will still get 300-ish. I have messed with all the LAN settings, updated drivers, uninstalled them completely and reinstalled them and then got fed up and bought a network card. Now the network card got the speeds I wanted but when first booting the computer the network card won't be recognized. I sometimes have to restart 3 times to get it to find the network card. Starting to wonder if it is the motherboard altogether. Anyone have a similar problem? I am still hoping it is a setting somewhere that is off