I am trying to get my tremolo picking on the low strings good and tight, to play some metal songs. Is there anything I can do to work on it?
practice it slowly to a METRONOME! and gradually increase the speeds to the desired obliterating gutteral sound you wish.
try holding your pick differently.

I hold it sideways so the side (edge) of the pick is facing towards the floor. it makes the strokes alot easier.

Try that or start of slow and just get faster, I can trem pick normally or my usual way now