I live in a two stories building. I have the cable modem setup at the basement connecting with a Time Machine. Then on the second floor I have an Airport Extreme setup at one end and an Airport Express at the other end. They were setup as an extenders. I set the network using 5GHz N only. But my network still drops from time to time and sometimes surfing the web is extremely slow, so I have to unplug and replug the routers downstairs in order to get back the regular speed. Is this normal? Is setting up too many extenders a problem? I am renting an old Motorola cable modem from Comcast. If I purchase a newer modem myself, will I see drastic improvement on internet speed?