rhythm guitar, need help with my picking hand

hey guys sup? i'm new here, this is my first post.
My name is Angelos.

I need some help. I have trouble trying to play fast, it's because I'm not holding the pick right, I know, but I tried different ways and still can't improve. For example, some Linkin Park songs require real fast palm muted upstrokes-downstrokes, I can't do that, downstrokes (direction down, right? just in case) are easy, but upstrokes usually move my pick in my hand and in the end I even drop it if I keep playing. or even with no palm muting, smells like teen spirit for example.

I can play that, but I have to hold the pick "wrong".

help please?

How exactly are you holding the pick wrong? Hold it relaxed, but still tight, and start playing the riffs slow at first. Try holding the pick in an angle, like when you're sliding the pick down the neck and doing the "scratch" sound, but not in that sahrp angle. It's hard to explain

I'm practising that kind of riffs now (but not Linkin Park, that's for sure...sorry :D), mostly Metallica riffs like Battery or Whiplash