cry for help

I've got my new Fedora Core 5 box all up and running wonderfully, except I can't get the modem (a 3com 5610 FaxModem) to connect at anything above 28800. It *does* connect, though, and all the links Google will pull up for me are for modems that aren't connecting at all (no mention of speed problems).

Anyone know enough about troubleshooting modems on linux to give me a hand?