Here's a few things I've noticed about getting more consistent and faster playing.
First of all you have to relax. The moment you start tensing up is the moment that you wont be able to play what you're trying to. Do you ever watch any really good players that don't even look like they are trying? Well that's because they really are barely trying. They can play relaxed and fast. Ideally you can get to playing blisteringly fast without expending much energy at all. When you start to get good at playing really fast it almost feels like you aren't even moving at all.
One of the keys to this is economy of motion. Watch your playing with both hands, are you making any movements that aren't necessary? From the sound of it you are. For example, you know that the shortest distance between any two points is a straight line. So the quickest way to travel that distance is a straight line.
So applying this thinking to your bass playing, when you're string crossing the only distance you actually have to move your fingers is the actual distance in a straight line between your strings. So any more movement than that is just wasted energy, and extra distance that is slowing you down. When you're playing on one string your plucking fingers have even less distance that you have to cover. If you are making exaggerated looking plucking strokes then you are just wasting tons of energy. Ideally plucking one string your fingers only have to move a millimeter or two to pluck and then reset to pluck again. So if you relax and just make the smallest movements possible you can get much, much faster. For example, lets say that currently your fingers move 2 cm in a full plucking stroke on a single string. If you can cut that distance to 2 mm theoretically you should be able to pluck 10 times as fast. Additionally you would only be using a tenth of the energy as before.
This also applies to your fretting hand as well. Any distance traveled away from the surface of the strings is wasted distance and energy. In fact, about the only time your fingers shouldn't be touching the strings is when you are moving your hand from one place to another to minimize the sliding noise. And even then they should be as close as possible to the strings. The only other time should be to let a specific finger have a note ring out. Ie when you fret with your index you need to slightly lift your other three fingers.
All of this actually does wonders for your consistency as well. Think about it, if you're making much larger movements then in the course of that movement there is a lot more that can go wrong. Instead if you are only moving the shortest distance possible to do what you need to there is going to be less deviation from one movement to the next.
In making these relaxed minimized movements there is one trade off, volume. Because you are attempting to use as little energy as possible you don't want to dig in, let your amp do the work. Crank it up so anything but the lightest touch rattles your houses foundation, forcing you to play softly. Once you get that down then you can expend a little extra energy to dig in a little bit more if you want. But even when you dig in try and keep your movements as concise as possible.
In summary don't move any more than you have to, don't use any more energy than you have to, and relax. Hope this helps some.
