My cat is a middle-aged outside cat (overnights she wanders our yard and the bike path). She never had any problems peeing or pooping outside the litter box before, but now she pooped, peed, puked, and is panting and moving very slowly.

We know its not rabies, as she got the shot for that a while ago. Whats happening? It all happened suddenly, this morning she was meowing and purring normally.

Even know your cat is acting normal now, I would take her into the vet anyways and tell the vet what has been happening, maybe she ate something that made her sick or maybe she has something more serious going on. I would take her to the vet, because you don't want this to recurr and you don't want it to get worse.

Good luck and hope your kitty feels better!

You need to go to an emergency vet now.

I'm hoping that you're saying your cat is back to normal now.
Panting/open mouth breathing is a HUGE indication that you've got an emergency on your hands. Your symptoms are pretty broad, although serious. What you're describing sounds like at some point your cat lost control of her bowels, vomited, and was in respiratory distress, which would indicate that you need a vet asap.
It sounds like whatever happened, the crisis is over, although I might consider a vet visit regardless to make sure your cat hasn't suffered organ damage.

ETA:

Vet Now. Respiratory distress is an emergency.