Networks Adjusting Up/Downstream power to Cable Modem?

My cable modem used to run at about -24dBmV Downstream and after removing a splitter it runs at about -20dBmV Downstream. The change in Downstream power took me from 45KB/s to 338KB/s.

I figured if adjusting it just 4dBmV made this much of a difference, perhaps getting it to the ideal -7dBmV would make me one happy cable internet subscriber.

I've heard adding an active splitter to it would help, and that DC Taps help with Upstream issues.... but I haven't found any information on what active splitters and DC Taps really are, not to mention where to get them.

Any ideas?

Oh, and my download speed jumped like crazy, but my upload is still dragging. Any tips on this would be appreciated as well.