Sustain comes from a variety of things... it might not just be your playing style... sustain can be lengthened by having more distortion or overdrive... more volume... having your pickups in the 'sweet spot' where they aren't too close to the strings to get natural distortion but just far enough away that they get the most sustain and natural tone... You might also not be hitting the notes clean enough or you might be muting the strings on accident somehow. What a lot of artists do when they tap... they use a delay effect to trick the ear into hearing more notes and more sustain than they are really playing. so try to play with a lot of overdrive and some distortion... also try to play as clean as you can. You might need to slow down a bit so you can play it more accuratly then work your way up. Good Luck!!