use your wrist for alternate picking, and when switching to other strings, extend or pull back on your elbow, you can get more stamina and speed with your wrist then you can with retarded unconventional muscle spasms from your forearm, it also helps for the angle of your picks attack for more heavyness go for an angled attack, for solos, have your pick flat or parallel to the strings to get the least string "talk" practice going fast
its also good to have the least possible movement from one string to the other...economy picking-evilness(sweeping is another story)