I've found that my technique will plateu for a while, then all of a sudden I'll find myself on a higher level. I think it's more a matter of letting go and just doing what makes you happy. Excersies are important, but if you aren't happy with what you're doing then what's the point?

Try and find new ways to push yourself, try and do things you've never thought of before, make up little riffs that are just a tad over your head and practice them until you can do them fluidly. You'll find that the overall speed will happen without you realizing it.

Also, since you're talking about shred, I assume you have a guitar with light strings... if so get a second guitar that may be cheap, but plays well. String it with .011s or .012s and practice on it. Go back to your main intrument and you'll find yourself significantly faster and that you dance across the fretboard effortlessly. Hand strength is very critical to guitar, especially as you do more technical playing.