Contact your ISP to verify that the number you are dialling supports V.90/V.92 speeds.
Contact your telephone company to verify that the telephone line for your modem supports V.90/V.92 speeds.
Line interference or the routing of the telephone call to your ISP may be causing a slower connection speed. Try placing the call again.
Verify that the modem is connecting to a V.90/V.92 server. A pair of 56K modems will not connect to each other at 56K speeds.