#1
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.
#2
Practice your picking and maybe string skipping.

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