Rather than continuously trying to blast through the whole thing, try this etude I've created... it nails just about every possible problem spot you might have. It's an etude with attitude; and attetude?Take a gander and MIND THE PICK DIRECTIONS, OR BE SMITED BY THE GODS OF SHRED:
Now here's the heartbreaking news... you are going to be limited in how fast you can play the initial scale by whatever is the hardest (slowest/least clean) part of this etude for you. For example, let's say you can play the first 2 beats worth of notes (A B C D E, down up down up down) over and over again at 200bpm... well, that's just swell! But when you get to beats 3 and 4, D E F G A starting with an UPSTROKE, you start sucking all over the place and can't break 140bpm without sounding like Vernon Reid. What that tells you is that you can't play that scale cleanly faster than 140bpm, and that sucks!
Disheartening? Don't let it be. In fact, be heartened, if there is such a word, because now that you know WHERE you suck, you can fix it far faster than before. Everytime you've run through this scale, "practicing" it from beginning to end, you've made the part you're already strong at stronger, while trying to force the hard part to catch up. This is little more than a highly effective way to waste your time. Take the part you suck at (whatever it is), drill THAT hard, and only then play through the entire scale a handful of times... notice how much better it sounds? You're welcome.
One final thing to take a look at, a Paul Gilbert idea taken to extremes. Rather than play notes at all, we'll take the left hand out of the equation entirely. Lay your fingers across the strings to mute them, and try this:
We are picking the exact sequence for the Am scale, but now we can know without a doubt if there is a right hand issue. If you can rip through this, then your left hand is actually the problem (I'll cover strategies for that soon), but if you can't, get to work!