Clogged Cat? Bad gas mileage?

I have an 07 DCab Pre-Runner TRD Sport.. 28,000 miles on it, K&N 63 Series Air Intake.. I get 13 mpg. I live in a really hilly area and I'm always going up and down hill (Palos Verdes, California) but I feel like my gas mileage is terrible. Someone thought it might be a clogged cat.. anyone have any thoughts? How would I check for a clogged cat? Thanks alot guys

 

In my experience when they start plugging up they make a nasty rotten egg smell and start making a different sounding exhaust.
With your mileage I doubt that's the problem. If your driving stop and go in those hills. Crenshaw and Hawthorne and so on, your mileage will suffer about like what you describe. I am sure I am heavier than you are but that is about what I get in the hills. However I just got a whopping 17.7 to and from San Diego. That is great mileage for me.

 

Clogged cat would feel like you have no power. Last car that I had with a clogged cat wouldnt rev past 3k.