When i play in dropped b (Dropped D 1 1/2 steps down) there are a lot of songs that require fast alternate picking of three strings. I pluck the strings once and then when I get stuck or something. If i switch to a pretty light pick it becomes a hell lot easier but I have weird feeling I may doing something wrong... Its funny because I can pick on string alternating extremely fast its just that when you incorporate one more strings I screw up like crazy. I need to get better at this for songs like The Blister Exists by Slipknot.
Practice your picking and maybe string skipping.

Also, if you think slipknot picking styles are hard, check out Paul Gilbert.