Slide is by definition pretty slow. You're using one finger so to speak instead of four. Also, the beauty of slide playing is long, flowing, vocal like notes and lines, not fast staccato notes. If fast and staccato is what you're after then slide is a stupid way to go about it.
However, for some songs you just need to be pretty fast with that thing. It's not that easy in closed positions (the first step to slide speed is of course hammering on and pulling off on open strings) but there are a few things that seem make it easier. Mainly it's about finding a smooth motion. Any other tips?
If you can't hear the others you're too loud, if you can't hear yourself you've gone deaf