Intermittent signal

Hello.  I recently replaced my modem with a Nighthawk CM3000.  Since that time, I have been having intermittent disconnection issues.  While playing a game online, the internet will freeze for approx 1 second every 2 minutes or so.  I'm also having problems with my WIFI signal  on mobile and often reloading websites freezes until I turn off WIFI.  I realize that may be a separate issue but it started occurring at the same time.  I had an old splitter that the Xfinity tech installed years ago to connect my cable box but I no longer have the box, or a need for the splitter.  I removed the splitter and connected the cable directly to the modem and I can't get an internet signal.  Any ideas?

Problems:

Intermittent signal

No internet when removing splitter