catalytic converter and fuel pump

Help!!

I have a 2000 gmc jimmy and it rattled a lot when i was stopped at a light. I took it in cuz the engine light was on and they said there was something wrong with the fuel pump and they needed to replace it. How exactly can you tell your fuel pump is bad? Are there any obvios signs? Also, they said the rattling was the catylitic converter and that it needed replacing also. Does that cause the car to run really poorly as in a big loss of power? Please help

a broken apart convertor will rob power faster than almost anything else because it increases exhaust backpressure. the fuel pump is checked with a fuel pressure gage. it's not very common on your vehicle for the fuel pump to affect performance. it's very common for the fuel pump to outright die causing a no start. what you should do is have the convertor replaced as well as fuel filter. another thing to be aware of is when a convertor breaks apart internaly it's possible for chunks to get lodged in the muffler but most times just the convertor gets plugged.
good luck

Replace the cat, leave the fuel pump alone and have them replace the fuel filter.