Yes, try replacing the Bank 2 Upper Sensor for the P1151 code.

http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=trouble&Number=1236165&Forum=trouble&Words=1151&Match=Entire%20Phrase&Searchpage=0&Limit=25&Old=6months&Main=1235635&Search=true#Post1236165

As for the P0420, it comes back again, then try mileliminators for the Bank 1 Lower O2 sensor.

"Always do the cheap and easy ones first." 1996 V6 ATX 96K miles