2004 Dodge Neon sputtering

When my car hits 2,000 rpms my car starts to sputter, almost feeling like we're running out of gas. I have been told that it is the catalytic converter. I was also told that when is starts acting up to pull over where I am and stick my hand behind the muffler. They said that if it was sputtering or not pushing anything out that it was the converter. I was driving it earlier and I just kept pushing the gas and it shot up to 3,000 rpms and then it just shuts down. But while it jumped up to 3,000 rpms, you could hear the air coming out of the muffler like it was having trouble coming out. What could be wrong with this car?