I had Comcast out this week for my chronic connectivity issues.
The tech said the Motorola modems (mine's a Surfboard 5100) are set to
shut themselves off at 54dB upstream. When the upstream power is high,
says my tech, the problem is at the pole and Comcast needs to come out
and 'rebalance' their side. So while going to a tap (good suggestion!)
or disconnecting your splitter will buy you a few dB to stay online,
you need to get Comcast out there to do their side of the pole.

I demanded a second cable drop (a dedicated coax run from the pole to
my modem, separate from the TV cable into my house) last year when I
had similarly frustrating cable issues.

The good news: Verizon is wiring my neighborhood (Livingston, NJ) for
fiber-to-the-house, and should be turning on the switch for their
verizonfios service here in the next two months, according to the techs
working on the street. As soon as that happens, it's goodbye Comcast
for me. Say what you will about the phone company, but my dial tone
never drops, and my cable is out at least twice a month. Ciao,