Sputtering car

My car is sputtering like crazy at all speeds. It will lighten just a but once I hit 6,000 rpms but its pretty consistent. I am no exhaust expert but there is a canister type thing after my cat (i belive it to be an interior muffler or a resonator) there is a rust hole in that would that cuase sputtering becuase of the pressure change. (Greddy exhaust). Also my fuel pump is eratic so Im changing that, wondering if that could be another cause. Any input would be great. Thank you.