Practice scales going up and down the neck using double picking. A metronome will allow you to focus on tempo. Slowly build up the speed. To get 'crazy' speed like Satch, The Jonezter, Vai, Marcel Coenen or whoever, it's going to require massive discipline. As your muscles develop, your speed improves. The picking hand and the fretting hand must be in complete unison; one cannot be faster than the other. Hope that helps.