How long have you been running the splitter setup?

With my previous provider I had to have separate lines, one for the TV tuner card, one for the cable modem, or it would drop the connection frequently.

I recall trying a signal amplifier before but that did not work at all for the data connection - it did improve the TV signal though.

Like Nick I replaced my modem with a Motorola Surfboard and it's been very good to me.

Cheers
KGG