(from an earlier item)The little information I have on USB and modems is that your USB ports will deliver 500m/amps of power with a +/- of 5 m/amps. The Voyager modem is a good quality modem but at times will require the full 500 or slightly more.
If your USB is only providing 495 m/amps this will lead to your connection dropping. One way round this is to buy a Powered hub. Connect the modem to the hub and the hub to one of your existing USB ports. This will provide full power to the modem at all times and give you an extra 3 ports to use as well. Cost approximately £20.00.
As for the speed i agree with Djohn check your line or ring your isp they should be able to test it for you,some isps like BT give you a Help test that you can run online and if it finds problems it tries to revert back to your old settings,the ones it took when you set it up first time around.