Make sure you don't have any splitters from the main cable line to any TV's to your modem..I don't know the exact numbers but ever split decreases your speed... I didn't know it made much difference until we had a bad storm and the cable guy had to replace my outside line which had a 3 way splitter..and I told him I had Cable internet and he put some kind of meter on the line running to my modem (the signal sucked) so he ran a separate line for me directly from the "Main" cable line..
I was shocked at the speed increase..
bobv