engine stalling issue

i bought this 97 tacoma in feb. both heads were cracked, had them repaired, and completly went thru the engine, and clutch assembly replaced fuel pump, strainer, wire harness, and fliter. after 2000 miles it has started to stall while driving. got the p0420 code replaced o2 sensor before cat. convertor, inspected cat. and it is clear reinstalled. reset code and ran it for about 40 miles and code came back. took truck to toyota and had them check it, they said to replace cat. convertor. I replaced o2 sensor after cat. and ran it for about 25 miles before it started stalling or bogging down again. i just don't see how it could be cat. i could be wrong. what else could it be?

 

That PO420 is that the 2 sensors are not seeing enough variation between the front and rear sensor.

Telling you the Cat or Cats are no longer doing their job good enough to please the ECM

We all go for the cheaper options first rear sensor

look for exhaust leaks a leaking gasket between the sensors can cause the MIL to trip

It can also be in the wiring or the ECM

I can only hope all that was checked by the dealer techs and eliminated

Leaving the Cat or Cats