Looking for modem upgrade

Looking for upgrade for motorola 56K voice modem dated oct 98 .

My ISP has recommended upgrading my modem as a start to troubleshooting a problem with wildly fluctuating connection times.
For a short time this afternoon I was hooked up at 4800bps. Thats right only 2 zeros.
It can fluctuate anywhere from 11K to 44k.
Anyone know where I can find a free upgrade to a newer version?

www.driverguide.com would be good place to start

USER NAME is: drivers
PASSWORD is: all
FWIW upgrading your v.90 modem to the latest driver set is not all that likely to solve a connection rate issue that severe. Line quality may also be a place to look or the ISP might simply have some flaky modems in the dial in bank.