is your board waxed? if ur base is really dry then that will def slow you down a lot.
another key thing is that even though you may have no problem transitioning from one edge to the other, you prob shed a lot of speed by doing skidded turns. as ur cruising down, try not to lean too far back on your rear leg. You want to keep your body perpendicular to your board. Lean as far forward as you can and even though you will think you are hanging over the nose of your board, youre really not, in fact the steeper the hill is the more you have to lean in order to keep that 90 degree postion.
Without me, my board is useless. Without my board, I am useless