I have a 95 pathfinder ,for some timeI've noticed that my Pathfinder has been really under power , my mileage is through the roof and going up hills seems to be quite a workout . New plugs ,new fuel filter ,new air filter , nothing seems to make a difference , however , someone mentioned to me about the catylitic converter may be plugged . How can you tell and what else do you do to find out if it is the cat.

 

check for Codes. A bad knock sensor could rob your power also and it does not trigger a Check engine light.