... is that your ISP is using non-V.90 modems or V.90 modems that are not compatible with your modem.

Like if they are using V.90/X2 3Com/USR modems and you, say, have a Lucent V.90/KFlex modem in your laptop, it could very well be the modems not handshaking at v.90 and negotionating a lower speed?

Cross out the V.90 and they handshake at the KFlex protocol at a higher speed?

Boggle?