What sort of speed is the speed test reporting? A lot of the "Slower than..." "Faster than..." statistics on site such as speedtest.net has a very sharp curve as to how much speed it takes to change a value. When you get into the 4-5Mbbps range you'll find that a single kilobit will change that value a good amount.
Ronbon it would help to see a post of your modem stats. Also do you know how far you live from the central office? If you are more than 3 miles away there is not a lot that can be done as far as I know. It would also help to know the make and model of your modem/router and any other devices you have hooked up such as a bridged modem
