Ethernet speed

I have AT&T Fiber and I get >900 Mbps over ethernet on an iMac located on the first floor, but on my laptop on the second floor I only get around 60 Mbps. I've checked all of the settings in the gateway and the equipment is new and designed to handle those speeds. I thought it must be the cable running from the gateway to the second machine, so I replaced it with new CAT6 cable; however, the speeds are the same - no change. Appreciate any suggestions.