testing coax cable/ packet drops

Hello I am a online game gamer and for a 2 week I have been getting packet drops and correspond to getting lag in my games.

one of the suggestion is that you should have your coax cable and splitter checked, but I have no means to check these, if I can get a comcast tech can they test the cables and splitter( which I believe is out side the condo)?

I know the problem is between my firewall wan port and the first pingable device on my packets going out. so firewall wan port->cable modem(arris s34)->the gateway->pingable address.

Also my arris tells me it has sync timing synchronization errors.

so I believe it is either my modem or coax cables, I have an old ARRIS / Motorola SurfBoard SB6141 DOCSIS 3.0 that I could try and reconnect to see if it the modem, but that uses old tech, so might not help, what do people think.

thanks