Yeah, like check the signal conditions at the modem -- I can point you at a FAQ for that if you don't otherwise have the info on how to interpret the many numbers.

But also check the firmware versions of the modem versus what the ISP recommends/requires. Most Cable ISPs will auto-update the modems to correct firmware, but not all of them. And there are known modem/firmware combinations that cause trouble in the presence of higher channel-bonding situations. The primary symptoms of which are random disconnects.

Cheers