My 97 Expy, 5.4 has 117,000 miles on it and I've owned it since 83,000 miles. The exhaust is stock but not sure if it has ever been replaced. When should I be concerned about the cats needing to be replaced?

 

I have a 1997 F-150 and i have done alot to my exhaust. All of it was stuff that i wanted to do......nothing was done to fix any thing. I had took my cats off to make my truck louder. Before I took them off they were workin fine and I have never heard anything about having to replace them. My truck had 109400 miles on it when i took them off and its still goin hard.