Comcast connection times out frequently, without cause.

Connection times out at random intervals, regardless of activity. For 3 weeks now, the connection magically times out when I try to get to any media-rich site or download any files. Technical support reps have managed to infuriate me by not documenting calls or troubleshooting steps taken or anything at all, for that matter.

I've replaced the only splitter in the line before my cable modem 4 times now.
I've replaced the cable that goes to my cable modem twice.
I've replaced the cable modem with a new one (Linksys CM100).
I've connected my cable modem directly to my computer (Dell Vostro 1500 laptop).
I've connected my cable modem to 3 different routers (Netgear WGR614v2, Linksys WRT54Gv2 and a DD-WRT x86 box built by myself.)

All that and nothing has changed.

I've had a truck out. The tech from the truck, in a stupefied tone, said "It's gotta be the splitter in the line before the cable modem", he replaced it and before I could contradict him, he was speeding off. He had no clue so he blamed the most innocuous thing he could and bailed.

None of the tech support people have documented anything I've done or said. At this point, the call needs to be escalated to someone who knows what they're doing, but I get nowhere.