Your cat could still be plugged..
Sometimes a way to tell is to bang on the muffler and see if anything rattles within it, like some pieces of the cat that have come out into the muffler..
But how far are you from a muffler shop? Most places will look at your exhaust system for free, to get an estimate.
Here's some steps I found on about.com:
Engine hesitates:
When you step on the gas, the engine seems to bog down or takes a second to respond.
You may notice a general lack of power. You may notice the problem when the engine is hot or cold or when you are low on fuel.
1. You may have a dirty air filter: Replace air filter
2. The spark plugs may be dirty or worn: Clean or replace spark plugs
3. The spark wires may be bad: Replace spark plug wires.
4. There may be some other type of ignition problem: Bad ignition module, distributor pick up. An engine scope is the best way to diagnose an ignition problem.
5. If you have a carburetor, you may have a bad accelerator pump or power circuit: Overhaul or replace carburetor.
6. The fuel filter may be clogged: Replace fuel filter.
7. You may have water in the gasoline: Drain tank and refill with fresh, clean gasoline.
8. Your catalytic converter may be clogged: Replace catalytic converter.
