Model C6300 wont work if I leave more than five freet from the Modem/Router

I purchased the C6300, had a technician install it, and had the cable company bridge the connection. It works great....except when I leave the room where the router/modem, an then there is no connection. Meanwhile, there is a strong signal.I tried diagnostics on the genie and there appeared to be no issue. How do I make it so that when I leave the room where the modem/router is, I stay connected? Right now, I am using the old internet connection to be able to write on this forum.