Codes P0171, 174, 430, 300, 303, 305

P0171 - System too Lean (Bank 1).
P0174 - System too Lean (Bank 2).
P0300 - Random/Multiple Cylinder Misfire Detected.
P0303 - Cylinder 3 Misfire Detected.
P0305 - Cylinder 5 Misfire Detected.
P0430 - Catalyst System Efficiency Below Threshold (Bank 2).

Did you erase the fault codes after replacing the spark plugs?

The computer controls are responsible for the engine burning the fuel as cleanly as possible. Since there will always still be a little undesirable emissions, the catalytic converters are added to address that. The first five fault codes refer to the emissions the engine is developing. Only the last code, 430, refers to a catalytic converter that was likely damaged by the other problems. Rather than replace the converter and risk the same damage occurring to it, address the cause of the problem first.

A common problem on Ford products has been weak ignition coils. If one cannot develop the voltage needed to fire a spark plug, a misfire will occur, then the unburned air and gas goes into the exhaust system. The unburned oxygen is detected as the "lean" condition, (codes 171 and 174), but you might smell the unburned gas at the tail pipe as a "rich" condition. The unburned fuel will also burn much to hot in the catalytic converter and overheat it. The catalyst can melt into a glob that restricts flow, and/or it can render it ineffective so it does not clean up the pollutants. That will result in code 430.

A simple test you can start with is to switch the ignition coils from cylinders three and five with two others, erase the codes, drive the car, then wait to see if misfire codes set for the same cylinders or the two you moved the suspect coils to. If the fault codes follow the ignition coils, replace those, then erase the fault codes again.