Typical if you have an exhaust leak or no cat.
I have no cat and don't have that prob.
I would say exhaust leak mainly cause the o2 sensor would read improper
a cat shouldn't restrict unless it's plugged. I have tested lots of cats at work when I get vehicals in for lack of power it's one of the first things I check and we put on a exhaust back pressure gauge and if it's good you don't get any restriction till your extremely high in rpm range witch is usually due to the exhaust system to not the cat!!
and when I say high rpm I mean if you tach it out!! going for a good run with it