I just recently started playing guitar (for about a month now), and I've been using a mixture of Rocksmith and Youtube videos to teach myself. I wouldn't quite say I'm decent, but I'm okay considering how long I've been playing. For practice, I just find a metronome on Youtube at 60bpm and alternate pick up to the 12th fret on each string and work my way up. However, I do notice that when I get to about 100bpm, I notice that I'm still holding the pick the same way, but I barely use any of the pick on the strings. I only use the tip of it, really. Also, I can alternate pick at 100bpm, just not consistently. So I'm just wondering if this is a bad habit that I need to correct or if I'm just going about practing wrong all together.
Take a video of you playing if you want feedback, we cant know for sure if there's a problem. Also, get a teacher.
But boys will be boys and girls have those eyes
that'll cut you to ribbons, sometimes
and all you can do is just wait by the moon
and bleed if it's what she says you ought to do
if you find you get to a speed you can't play consistantly at, in your case 100 bpm, turn the metranome down a bit and practice some more, eventually you will be able to play at that speed, it just takes time. On an off topic note, I would suggest learning notes of the guitar, and getting a metranome
Camera isn't being cooperative right now, sorry >:| But anyways, I've also notice that I tend to make a sort of fist when I start Picking at "higher" speeds.
To pick fast you actually have to pick at an angle, not the way you would at a slower speed. So yes, you will find your self using mostly the tip of the pick because the pick doesn't have time to dive itself in like it would at slower speeds.

Now, for the not being able to pick consistently, practice.