Need Help

[KickerGrandPrix]

I have a 06 grand prix and when i get on highway i get a smell but i still have full power. I have some shops tell me its the cat and some that tells me its not. is there anyway to test if the cat is bad or not.

 

[SlowNA06]

i get a smell

Describe the smell, padawan.

 

[KickerGrandPrix]

its bad smelling like rotten food. but its only when i get on interstate.

 

[SlowNA06]

Rotten eggs? Sulfur? That's a bad cat. They're good for like 150,000 miles, typically.