03 expy stutters when excelerating slightly checked codes have a p0125 and p0420 how to fix?

[Kingofcali]

Can a p0125 cause the mis fire stuttering?

 

[Grover6]

google says the P0125 code the ecm not reading enough heat in the coolant system, and the P0420 is a O2 sensor. can't confirm that would cause stuttering, but seems like a likely outcome

 

[TobyU]

An 0420 is not a bad O2 sensor it is one doing it's job and reporting the output after the converter is not enough reduction than the input.
Catalyst below threshold efficiency.
Means weak converter often but regular misses will load up the exhaust and cause it too.
Look in test results for misfire counts and see which cyls show increased numbers and then clear codes and check the misfire counts later.
You need to see repeatedly which cyls are misfiring.
Or just put new plugs and COPS in it. They are $30-35 a set on ebay and even on FB marketplace.
The other code could be a bad coolant temp sensor or unplugged one. Usually in intake water passage. Could be two of them. One often does the gauge and another gives ecm info. Not sure if yours does that without looking under hood.