or if god hates you and you really weren't meant to play guitar. But either way good luck
Heh! Heaven has nothing to do with us!
Seriously though this a problem I encountered and I nearly quit because of the sheer frustration it was causing me. I focused on it obsessively playing nothing but exercises for three hours a day and getting nowhere...
The problem was that the more I focused the more 'rigid' my playing became. My little finger on my left hand became an anchor and I directed all motion through my thumb and fore finger instead of letting it come naturally from whatever muscles on my entire arm the piece I was playing required. Because my hand was so static in rested pretty much firmly on the bridge.
It was a vicious circle: The more I practised the more rigid I became. It wasn't too long before I capped myself at 150 bpm. solos that I had played before at say 180 were almost impossible.
The key I found was to relax. There is no one right way. Individual pieces of lead require a different level of 'tightness' in your right hand. If you don't tuck your little finger in then let it hang loose providing only support on the scratch plate area IF you need it. That's not to say that it can't touch it just don't let it anchor your hand. Dont be afraid to adjust your hand especially when running through scales. Don't be afraid to add some weight or movement with your arm.
There were three actual Techniques (other than exercises) I used to get speed back.
!: Trem pick. Like the man said above if you can't play one note fast you'll never play a scale. It also helps keep you hand from being planted to the bridge. Use a metronome and just start at say 80bps and work your way up. When you find a level your struggling with, knock up the metronome a few levels and attempt that for a couple of minutes then go back and try the original speed. Sometimes it just helps to push you limits.
2: Do NOT neglect other styles. Arpeggios and String skipping with help keep your playing fluid. If you play scales for three hours a day and nothing more not only will you not be able to play anything else but you WILL stunt the growth of your speed as well. Holding a pick is not a natural process and your fingers need to get accosmed to it, you need to develop muscles that your body does not necessaily use in any other process than playing guitar. You need to able to 'pick up that pick' in such a way that it becomes a natural extention of your body that means it needs to grow beyond the extremley narrow 'up down' reflex you will be enforcing. Alter the environment even slightly (posture, sweat, temperture, grip, style etc) and your techinique will NOT adapt and this will frustrate you. The more varied your style, the faster you will grow as a speed player. Also the human brain assimilates information at a set pace; it takes an adult an average of 15 minutes to learn something and process it. Which means the majority of a three hour practice period where all you do is play the same exercises is going to be wasted.
3: Play standing up: This will increase the variables in your playing and allow your technique to adapt shaping you into a much more of a 'natural' player. This process starts off slow, it is more difficult to learn something standing up but I cannot recommend enough the need to practice standing up. The main reason for this is that while you are effectivley training your right hand to play at a certain angle, in a certain position, with a certain amount of weight displaced then as soon as you stand up this all changes enough to significantly lower the standard of your playing.
Hope this helps I have a few more tips but I think I've rambled on enough!
Stay Metal!