The superhub is junk as you have just found out. Sticking with modem mode is your best bet by far.
However if you
really want to fiddle with the superhub try:
Making sure your band is 2.4Ghz and your mode is 145Mbps, download and install
InSSider and manually select the channel that gives you the lowest RSSI value.
The superhub wireless is weak and super sensitive to interference. Someone in your locality has probably started transmitting on the same channel as you with a strong signal which is killing your superhub.
Good luck