Erratic (at times) WiFi / Shuts off/Turns on periodically

Okay, so I do not rent or use the Comcast/Xfinity Modem, but use a NETGEAR CG3000Dv2 Gateway for years. Comcast is recommending that I upgrade to a newer model Gateway or rent one of their models. However, this modem still works great except at times (it could be days/weeks) that I have no issues then all of a sudden the WiFi goes out then mysteriously comes back on soon after then stays on for days on end. I used to unplug the modem and reconnect and wait but it would not fix the issue. Comcast said the signal looks good on their end, so I decided to replace the 2 outside cable splitters and thought that was my problem, WiFi has been working great, then all of a sudden it starts again, WiFi shuts down then later when I leave the modem untouched the WiFi returns! Is COMCAST messing with me in order to make me rent one of their Gateways???