Ok - when I strum normally, I relax my wrist and hardly mre my elbow at all. To strum fast, try tensing the wrist and then letting the elbow go into spasms. At first this sounds like it'd slow you down, but especially if just hitting one or two strings, this technique can help you go faster.

As for up strokes - are you using a plectrum? How thick is it? I guess you've just got to look at the angle that you hole the pick at for a down stroke, and try and replicate this in reverse on the way up. Does that make sense. Give it a try and get back to me.

JE