when i strum chords really ****in fast my pick always slides out of place and i cant control it for too long. what can i do the prevent this. ive tried a few ways but it doenst help.
get brain picks, check them out

they have like this scratchy surface that really keeps them in place
peavey vypyr 30
yamaha starter guitar
Agile AL-2000 Tribal Blue


A God Has Fallen,
R.I.P. Dio!

why Scorpions Why!?!
yeah a new pick with either more grip on it or the thumb thing would be a good solution
Nylon picks. They have a grippy upper section, works fine for me. Unless you hold the pick inverted, in which case you will get an annoying scratchy noise from the grip.
I also have the same problem. I use a maestro pick(Hard, and thick) as my normal one. It slides a LOT, though.

I've tested out a fender heavy, and a clayton heavy as well. The clayton has pretty lousy grip, while the fender seems to have the best grip.

The only problem is, they all slide! Even when I switch picks, they slide.
That'll fix with practice, don't worry.
You must be relatively new to guitar or tremolo picking.
Try slanting your pick a bit.