modem problem

Greetings, all -- utter novice here. I have a Dell Dimension 700 w/ an
internal USR 56K modem, running Win98. I have never been able to get the
modem to connect at a speed higher than 168000 bps, even though it's a 56K
modem. I know one never gets a true 56K connection, but I would think I
could at least get 40K. I've tested my phone line by connecting thru the
same jack with another computer (signed on easily at 50K bps), and the
configuration settings for the modem are set to my ISP's preferences
correctly. I've tried several of the most common INIT strings, with no
luck. Is my modem just dying? Or is there some configuration variable that
I'm overlooking? The ports are set to maximum bps of 115K, there are no
conflicts shown in device manager, and port and IRQ settings are to standard
default parameters. The laptop is set up with Win 98 also, and all the
networking settings are identical to this machine, but it's a different type
of modem (Win LT fax modem(?) I think). I've always heard that USR modems
are pretty reliable -- however this one may be a couple of years old, so
it's possible that it's wearing out. However, I don't want to go buy
another one if there's something simple that I'm overlooking, and especially
if the problem isn't the modem. Any ideas? Thanks -- M9