This isn’t really “pickslanting” in the sense that we use the term when we look at things like Joscho’s alternate picking. In these examples, the fact that pick changes its orientation in space is unavoidable because you are using forearm rotation as a source of picking motion. That’s just the way the forearm works. The pick may appear differently oriented at the top of the strum than at the bottom, and may even appear to have the “wrong” pickslant for the way it’s going, hitting up-strums with what looks like a “downward pickslant”, for example. Try not to be too concerned with that.
The main thing is that you are using a combination of forearm and wrist here because you want to move the pick in a vertical direciton that covers a lot of distance — all six strings — with a fair amount of power, and those two joints combined is how you do that.
All the examples on our site play in slow motion by switching the recording to the slow-motion camera. You can get an additional 50% slower with the speed slider. The slider itself is not how you enable the really slow motion though - just remember to switch the recording. You can of course pause at any point.
SoundSlice may have a frame advance control, I don’t know. Otherwise we sell download copies separately, but I don’t think it’s really necessary for something like this to see a frame advance. What you’re trying to do here is actually a big, fluid thing, not a “tiny adjustments” kind of thing. The best way to learn this is to experiment with making large, fluid motions that feel fast to you, and to notice when it begins to feel smooth. You can refer to the video once in a while but try not obsess on small spatial orientations at first - the bigness and smoothness of the motions is where it’s at.