I don't know how wualified I am to give MA but I'll throw in my 2 cents anyways. Your vids were fun to watch.
The big things I saw were your late turns and the tuck.
Turns: I think you could try to initiate your turn a little earlier and hold it a little longer to be able to do so on the next turn. This, I believe, will allow you to carve more rather than skid, and give you less loss of speed. Leaning forward a tad bit more would help as well.
Tuck: It's really not all that effective if you're just standing up like that. I see that you are not making a common mistake: you know to hold your hands up in your face, rather than down by your sides. However, either get rid of it or try to lower down so that your head is the only point on your torso that is touching air. Modern ski racing has a great article that I really used and I think has helped my tuck a lot. In the little animations, see how the figure had his head really low, hands up by the chin (which you are already doing nicely), and elbows even down by his knees. The main point is elongating yourself parallel to the hill rather than perpendicular to it. But the article also deals with knowing when to use the tuck, and I think you might cross it off your list entirely for a course that tight.
Here's that article:http://www.modernskiracing.com/Bully.php