2004 Chrysler Pacifica Cat converter

Engine Performance problem
2004 Chrysler Pacifica 6 cyl Front Wheel Drive Automatic 74000+ miles

I recently have had my fuel pumps, timing belt, water pump, timing belt tensioner replaced. When I received the vehicle it ran fine for about twenty minutes for the ride home then the check engine light came back on again except it is now blinking instead of solid. I had the codes read and the codes shown were 0300, 562, 172. I know P0300 may mean that there is a misfire 562 is low voltage 172 a rich condition called mechanic up he says its the cat converter. Vehicle runs ok for twenty minutes then starts bucking like a bronco could the cat have gone bad or is mechanic hustling me.