= Impossible?
Well hopefully not, but I haven’t been able to find a way to combine these three components.
To give a concrete example I recently encountered, check out the chorus of Metallica’s Damage Inc. found on Songsterr (see bar 75). The tempo is 180bpm and it’s two full bars of 16th note power chords. (Disclaimer: It’s possible the tab is wrong, but my question still stands)
Palm Muting + Alternate Picking? Check 
- Personally, I use a typical wrist-deviation based USX motion with a downward pickslant, which allows for easy palm muting on single strings. Pick grip is somewhere in between trigger grip and extended trigger grip based on other pictures I’ve seen.
Palm Muting + Chords? Check
- The same motion works great as long as I’m only downpicking the chords.
Alternate Picking + Chords? Check
- A bit more awkward, but I can pronate my arm almost to the point of resting my thumb against the body, which produces a more neutral pickslant. Then I slightly supinate on downstrokes and slightly pronate on upstrokes to ensure all required strings are struck, while the primary motion is still wrist deviation.
Palm Muting + Alternate Picking + Chords? Not even close 
- The pronated position required for the previous combination makes palm muting physically impossible. If I try to use my regular wrist position so I can palm mute, the upstroke will skip the lower strings.
Any suggestions? Bonus points if it’s compatible with my current motions.