i can hold the gaspedal in one spot and my rpms jump up and down about 500 rpms, whats wrong ?
i have a 2001 GT 3800 II with 113000miles on it, i already replaced plugs wires coils, fuel pump and filter so im guessing a sensor is bad but there is no engine light on

and i am pretty sure my cat is clogged it rattles and smells like eggs on the highway

seems like you may have a torque converter lockup problem. does it drive normal when accelerating at lower speeds?

I believe I have the same problem possibly. With mine it feels like the car is struggle for power, and the problem is exaggerated on an incline. I have to get off the gas, then back on again so that the car shifts into a more powerful gear to get the power, otherwise, if I just held the gas without letting off it would just keep revving up and down. It might just be me, but it seems to occur more often during the winter months. Let me know if this is similar to your problem, if not sorry, but I'd still appreciate some help from anyone willing to offer .

if your cat is plugged the car will be sick for power and will be constantly going in and out of overdrive...when mine plugged it started with what felt like a high rpm miss and progressively got worse. Loss of power, weak acceleration, poor mileage,rapid heating under load, SES O2 sensor codes and what feels like misfiring are all big indicators the cat has problems. I truly feel that the factory "U"bend isa big cause of excess exhaust heat which eventually toasts the cat. If you have to replace the cat, get rid of that U bend for sure.

I just noticed this on the way to work this morning.

I attribute my symptoms to the new air intake system I put in though as I can put the stock airbox back in and the problem goes away.

It is not that big of a deal for me so I will live with it (especially since I am going to get new cat back to mufflers real soon and replace a possibly faulty cat)

I say replace the cat.