you can check to see if the network card settings are correct
you say your router “should” did you check to see what it was set at?
I am assuming there is no wireless in the mix ?
I know it is unlikely but do you have an old cat4 cable anywhere in the mix?
Are you using a network switch between the computers? Virtually all computers manufactured in the last eight to ten years have 1000Mbps (Gigabit) network adapters. However, as stated earlier, the computers will only run as fast as the slowest component. So, to run at the fastest speed between the computers, you should have Cat 5e (note the “e” for enhanced) cables and a gigabit network switch. While most newer routers have 100Mbps to 1000Mbps LAN ports, there are still some, including internet service provider gateways, that do run at slower speeds.
I don’t know how to check network cards. I figure if i bought a card that will run 100mbs and the other has a built in card at 100 mbs it would default to 100mbs. Yes its on wireless right now. No cat 4 anywhere. Logging into the Router shows it set at at least 150mbs.