When I do alternate picking on a single string or multiple strings without fretting with the left hand, it can be pretty fast, consistent and relaxed. But as soon as the left hand gets involved what was once smooth back and forth picking devolves into a kind of circular stab at the strings with tension coming into the right hand. Apparently my left hand has quite an effect on the motion of my right. It's similar to what happens on the first attempt at tapping your head and rubbing your belly at the same time. Eventually the motion morphs into an uncoordinated mess.
For the past week I've been really isolating the right hand action and trying to feel when and where it starts to break down. Funny enough, when the right hand is acting correctly the left seems to have no trouble keeping up.
I'd be interested to hear if anyone else has similar experiences or specific breakthroughs that have helped with speed.