Check engine codes PO420 and PO741.

What is your question?

The car is actually a Pontiac Vibe. I don't know the history of the car. I am looking to buy it from a friend who's daughter drove it to college. I drove it about 110 mikes yesterday. I put the scanner on it and got back PO 420 Catalyst efficiency below threshold and PO 741 Torque converter CKT Performance or Stuck Off. Car has 180,008 miles on it. Where should I start looking? I have felt a shudder once while slowing down from 70 mph. any help appreciated.