Q: Why would my Gas mileage be cut in half, Went from 400 miles on a tank of gas on 1997 Saturn SC1

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
Changed out fuel filter, Oxygen sensor, Crankshaft position sensor, to no avail, gas milage is still below normal. What next? Also deaccelerates when climbing hills. And acts like it has no power.
(1) Answer
(2) Comments
does not have to get hot for the cat to be clogged. have a shop do a backpressure check and a snap throttle check to verify