First thing I would check would be for a plugged exhaust or secondary convertor. Easy test would be to disconnect the system at the first flange behind the front convertor (two arrows) and just use one bolt to hold it to the side. Then a quick trip up/down the street to see if the power is back.
If you do not want to wake the town up you could do an exhaust back pressure test using a pressure gauge put into the first oxygen sensor port (one arrow S in exhaust manifold) and see what it shows. Ideally you want less than two pounds of pressure with the throttle open.
When the system gets plugged it acts the same way to the engine as if you catch a cold. Neither of you can breath. Because the exhaust cannot get out of the system fast it blocks the new fuel charge coming in and will be worse if you step on the throttle quickly.
Bunch of reading and more info on the testing.
https://www.2carpros.com/articles/how-to-test-a-catalytic-converter
https://www.2carpros.com/articles/bad-catalytic-converter-symptoms
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Friday, February 16th, 2018 AT 9:13 PM