The upstream power is marginal. Do those power levels remain stable to within 3-4 dB at all times ? To try to get a little more wiggle room, are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured ?
If there aren't any uneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then putting them back together again, then perhaps it's best to book a tech visit to investigate and correct.
