I had a rattle but the material was so crammed in there by the end it stopped and was plugging up the exhaust. Yours is probably moving around in there still which is why it gets better occasionally. Mine is a 4.4 but I doubt the cats are different. My engine has 130,000 so we're not far apart.

I knew the coils wasn't it because I swapped them and the misfire stayed put. I also swapped plugs around.

I'm afraid it will come back after the crap in them blocks the exhaust again.