Anyone got and tips on improving palm muting strumming speed?
Yeah. Do it.
just keep playing, itl come, also if your playen standing up keep our strap so the p/us are as high as where your hand is normally, who cares how it looks
make sure you're alternate picking rather than all downstrokes... that seems to be what slows down lots of people I know. Just keep practicing and you'll get it. Also, don't go for crazy fast speeds if you can't get it right, try playing it really slow and speed it up a bit each time.
just practice, if your trying to do really fast downstrokes it's gonna be harder, and take a little longer for your hand be comfortable with it.