@john2393 

First start with swapping the Ethernet cable out, being at 100 Mbps could be something with the cable, even with your computer getting normal speeds, something worth trying. If you have not done so already, I would factory default the router and leave all the settings as it, and see how that performs.

Test multiple devices to make sure the slowdown is not on the device.

@Tony thanks, i will try swaping the cable, the computer is conected directly to the modem and the speed is fine, so is either the cable or the router itself