Need more information on the layout of the house. Multi-storey? Single level? Is the modem located in the basement at the electrical panel or somewhere else? Is your PS4 hard wired straight in to a jack on the wall or going through a different device? It almost sounded like you had a provisioning issue but if your PC is getting full rates I'm leaning more towards bad WiFi due to modem location or bad wiring either with the terminations or unsupported router/device in between Modem and your other devices.