modem rebooting - new modem same problem - Fairfax VA

For several days my SA modem would lose connectivity, eventually rebooting (sometimes for 5-10 minutes at a time) until it settles down for a while. I just bought a new SB6121, and after installing it today, it has rebooted twice in 3 hours.

I think this is a signal issue. The only other thing I can think to do myself is swap the splitters outside (splits into TV room and internet room). Can I get a new splitter from the Cox solutions store? Any other ideas?