Toyota Repair: ongoing electrical problems, oxygen sensor, engine misfire

Question
Ted,
I do appreciate your past help.  You've been solving all of my issues this far.  I replaced the distribitor as per your suggestions, and the ECU error code did go away.  The engine runs great now!
However, there is another issue that I have not been able to resolve.  After I had fixed the distributor,  I re-checked the ECU error codes, and I received another one. Not only does the CHECK ENGINE light remain on when the truck is running; This time, it's telling me that there is a problem with the Oxygen sensor.  So far, I have checked all of the wiring for continuity, from the O2 sensor to the check connector and to the ECU. I have also replaced the O2 sensor, and the check engine light is still on, and the error code still says there is a problem.  

I really hope you can help.
..also, thanks for the wiring diagrams.

-=Dax=-  

Answer
The O2 sensor is normally not the cause of the light coming on, there is a possible mechanical problem with the engine that may be causing it to run too lean or too rich, this could be caused by something as simple as an intake air leak or a tight valve, so check for any leaks on the intake side and check the valve adjustment, also an exhaust leak can cause this code because the O2 sensor sees too much oxygen in the exhaust gas, there could also be an engine misfire at idle for some reason, on the more serious side there may be a leaking intake or exhaust valve, a compression test will show if that is the case, there could be a problem with the headgasket, start by looking at the basics first,I don't remember the context of your first posting so I may be repeating myself.
Make sure the spark plugs are good, and the wires, check for cracked intake air hoses, check the valve adjustment and the basic engine timing, if all the basic functions of the engine are good start looking for a more serious problem.