Is your car having these problems & not having CELs come on?
I would think it should with a bad cat or if it's misfiring bad enough to run that bad.

 

When it started again (@40k) I did get a flashing CEL at red line in 3rd. I ran it pretty hard the other day to see if I would get the CEL again this time, nothing... I'm gonna play it safe and order the duralast coils tonight and take it in to a muffler shop for a second opinion (as suggested here) asap. I did have a slight glow to the CAT @30k when I took it to mazda, they said it was nothing... I'm not convinced now.