I threw a P0420 code earlier this year and had our local exhaust shop put on a new converter. Problem solved.

Today, CEL illuminates with another P0420 but I am in business attire.

Question: Does the '03 4.7 have one converter or two? Could it possibly be a downstream O2 sensor?

 

My 03 has 1 converter. It's possible the rear o2 sensor is the cause. Without proper diagnosis that is just a guess. Check the link here. Check out what they say about after market converters.
http://www.obd-codes.com/p0420