please help

My 2002 grand am has a little ove 80000 miles on it. i bought it knowing it had a problem or two i got those fixed and it ran great for 3 or 4 months, last month i was driving around and noticed it was having trouble shifting after i got over 25-35 mph. i figured it was the transmission, i had a mechanic look at it he said the catalyc conver was plugged up and i needed a new one. well i came back up to school and took off the cat to see if that was the problem it still isnt running i took it in to work had some codes pulled and it said it was the egr valve i replaced that and its still not running, barely at all now it wont go above 10 mph and has very little power going to it. please if you have any idea wht it could be let me know i need my car and at the moment dont have any way to get in anywhere to get looked at.

thanks to anyone that can help.

did you put the cat back on and the down stream O2 sensor???
any other codes
What about new fuel filter
what about vaccum line check

yeah wont run worth a poop if you remove the Cat , or disconnect the O2. These models do have an EXTENDED warranty on the Cats becuase their were issues with 2000-2002 converters.

And your 80k miles falls with in the replacement range. ;)

and Welcome to AF toofast517 !!