After market catalytic converter causing engine overheating?

I have a 1995 4-runner that had the original Cat stolen/cut out. My local garage replaced it with an after market model. After replacing, the engine sounded a little off and after driving the car for 5 minutes the engine temp was really hot. I got the car home asap and the next day checked the level of radiator fluid and tried again. Again 5 min then the check engine light went on and I brought it home just as it got very hot again.



what do you think??

Whwn they cut the cat out, did they take the oxygen sensors with it? Was everything replaced?

One other thought is, did they use a proper part number aftermarket replacement or just a jury-rigged generic?

I will ask when i see the mechanic shortly. thanks