cant get the car to go 25mph or reach the 3 rpm on 2003 Chevrolet Malibu

i cant get the car to go more then 20 mph feels like something is clog will not shift and iam flooring the gas ... already check the trans filter and the cat car has 80k miles

Asked by for the 2003 Chevrolet Malibu
Many possibilities. Like you mention, the transmission and a plugged Cat will cause this. You could have other issues too, but first, have you checked to see if there is any diagnostic info stored in the engine control module?
no codes or check lights i deconnected the exhust from the cat and drive but still have problem cat looks good at the one end but did not remove the cat its self.. i also put the car on blocks and the car shift good and i can get it to 55 easy but when on street wont do 25mph?