2001 Other Mazda Models chugging and poor gas mileage

The P0301 02 and 03 means that there is a missfire on cylinders 1 2 and 3, if that is the case I would check the coils and injectors on those cylinders, also there compression.

Next I would change the the spark plugs and wires and that should cure that problem. You may also choose to check for vaccum leaks by starting the vehicle and spraying around the intake manifold with carb cleaner, if the idle changes you found a leak.

For the other code that means the catalytic converter, bank 2 is no good.

Chaange the converter and check the whole bank 2 for air leaks. Also may be a bad sensor or cut wire in the harness.