Thread: no power when accelerating/cant realy accelerate

I've got a 2002 grand prix. Itsa 3.8n/a engine. lately its been totally conking out for power going up hills or accelerateing onto a main road.
I gave it an oil change and some new plugs/wires since I had a car with a misfire once that behaved similarly; but that didnt help. at first i thought it was the transmission since it changed gears so much but now i'm thinking its something else. (not really used to an automatic)
If i put it in park and rev the engine i can go to about 4k rpms but if i give it a little more gas i can hear a clattering noise and the rpms go back down. i cant really pin down whats making the noise, though when i watch it idle i noticed the tensioner pulley (it looks like a tensioner pully atleast) kinda bobs up and down a little.
if anyone has had a problem like this before/ can point me to a thread it'd be much appreciated. i havent had teh check engine light come on at all and i'm sorta at a loss as to what to check next

yeah i just saw a 'clogged cat' thread was gunna edit my post. I'll try the MAF thing first. Is there anyway to test for a clogged cat or is it just a replace it and if it works it works kinda thing? also if it is the cat should i keep lookin for the root of the problem? i mean these things arent supposed to clog if everything is working right.... right?
i gotta dig through my files see if any of this stuff was replaced, the previous owner literally saved every oil change receipt

dont think it was the maf. without it plugged in it gets to 4100 lurches like i had amisfire and continues to do that. with the sensor plugged in it lurches and then the rpms go down (as opposed to revving and missing again)

As far as deleting the u-bend i can personally attest to this increasing the power somewhat being as how i recently had this done and had the resonator deleted. I noticed it as soon as I hit the gas to pull out of the exhaust shop parking lot. Thanks to the resonator being removed the exhaust is also noticeably louder as well. Now as far as the Cat. Converter goes it might be getting plugged up i would go to a reputable exhaust shop where you live and have them check it. If it plugs up completely it will leave you on the side of the road.

Hope this helps.

Someone PM'd me about this problem so I figured I'd update the thread.
I replaced my catalytic converter and it did solve my loss of power problem. However I bought an aftermarket one without doing my homework. The car runs fine but I am stuck with a periodic check engine light. the code is 'p402: catalyst below efficiency threshold bank 1' which from what I gather means the cat doesn't burn off enough of the bad stuff... I think. (I think the guys who run catless have found some sort of solution that tricks the sensor?) don't quote me on this.
Best of luck to anyone else having this problem.

The O2 emulators don't work on 01+ cars IIRC. Need to replace the cat w/ a stock flow version or tune it out. I know I've seen threads about Magnaflow high-flow cats causing this same issue.