Hi everyone. First, I’d like to thank Troy Grady for the tremendous amount of information he has shared and thank you to all the users on here helping each other. 
I have been struggling with alternate picking in general, but specifically when it comes to metal rhythms (thrash metal to be specific, your 16th note 000000)
From my understanding it looks like I use USX motion and I’m a natural downward slant player.
My issue is my up strokes get caught on the string and I feel like I’m fighting with the strings in general. I also tend to get tired/tense if I really want to speed up or for a longer period of time. There have been times I’m able to get a spurt of speed but only after 1 hr of playing. However that “fighting with the strings” is still there, not the effortless smooth picking we see our heroes use.
What I have tried:
I have used so many picks and settled on the standard Tortex 1.14mm. I have tried using “bridge lean” which didn’t work, I also switched using an upward slant position (think it was) but found it extremely uncomfortable to the point I was experiencing numbing and tingle sensations.
I also tried “strengthening my upstrokes” by picking only up, an advice I got from Paul Gilbert.
I hope you guys you can help.
Here’s a video.
Thank you and take care.