I had a stumbling problem on start up that went away within the first 45 sec of a cold start. I started to think the heater on my O2 sensors may have died so I made a test harness like described here:
https://www.motor.com/magazine-summa...cuit-failures/ Used a simple side marker light from an old harness and a plug from an O2 sensor from Pull a Part.
Turned out that the muffler shop must have left the O2 sensor in the pipe when welding my new exhaust. Seems the heat or the arc fried the sensors. Replaced with new Delco ones and have been great ever since.
You can read up on my saga here:
https://67-72chevytrucks.com/vboard/...=774609&page=3
Page 3 Post #58 is where I started the testing the heater circuit on the O2 sensors.