Lack of Power on Hills, 2000 Quest

I have a 2000 Quest that is losing power up hills to the point I can't even stay at the speed limit going up a hill on a freeway. I've replaced the spark plugs, the fuel filter, the cap & rotor, and the air filter. None of that has helped. Anyone have any idea what the problem is?

Changed out that c.converter
Changed out that c.converter - went for a test drive and I believe it's fixed! whoo hoo! Thanks for your great advice!!
lack of power
same thing happened to me last week. turns out it was a clogged, front catalytic converter. replaced it and i forgot how quick it used to be.
Thanks! Gonna give that a
Thanks! Gonna give that a shot.
u can check the efficiency of
u can check the efficiency of the cat/conv with one of those therm. multimters..it should be a certain temp before the cat and then a lower temp after the cat
1996 200sx se-r
2002 quest gle