I am intrigued by the "in half" statements.
As a guess, I would say to check the speed negotiation status of your NIC on your workstations. Sounds like AUTO isn't connecting in DUPLEX as it should. Take away the "negotiation" and set your NIC's to highest speed, DUPLEX manually. Also, don't use the AUTO speed settings in your router unless you have many workstations with different, usually legacy, hardware.
It is common for "auto" settings to not negotiate properly with various brands of hardware. When this happens manual settings are your best friend.