It shouldn't be split more than twice... the main feed from the box of the house should be going to a single splitter (one that doesn't degrade the db) and right to the cable modem... the other feed can be split off to the TV and fax or whatever.
What it sounds like is happening to me is the signal is dropping cause of the splitters - I'd run a straight line for a while to the modem and look at the levels of it using the modem signal page. If its not right and the tech put in a splitter to offset it instead of adjusting at the pole he/she is lazy and putting two inline to the modem is stupid.
Also make sure the line going from the main box to you're modem is RG-6 and not old 59 crap if it is 59 then either you replace it or have the tech run you off a stretch of it. If you can find a Sat co guy you know or something let them run you off some of that good copper they use for the satellite hook ups.
here is the modem page link