I know you said you checked and fixed a broken wire going to the o2...perhaps there are still issues with the wiring.
Good idea checking the temp sensors.
I see there is a "mod" done on the insights to help keep it in lean-burn as much as possible. It's a throttle position sensor "smoother". If your TPS isn't responding fully, or the signal isn't getting to the ECM, it might be keeping it in lean burn. Which I mentioned before, but don't remember if you checked it or anything.
Pretty much guaranteed it will stay out of lean burn without the O2 sensor telling it all is good, so even if the TPS isn't working, unplugging the O2 would keep it running in "normal" mode.
Of course, it could be totally unrelated. At least the TPS is easy to check...ignition just needs to be on, doesn't need to be running. Presumably a 5v signal that will vary according to how open the throttle is. Can check that it's getting said signal at the ECM too, if you find the right wire.
I think you said you checked/cleaned the EGR. I really should read back but...I'm lazy.
The code and behavior still point to the O2 though. TPS is a quick/easy check, then I'd go back to the o2. Still have +12v and ground at the heated circuit with the sensor plugged in? Not showing any weird voltages on it? Some resistance on the +12v side would end up with lower voltage or voltage falling flat on it's face when it's loaded/plugged in. Resistance on teh ground side would end up with a + voltage reading (more than a couple of hundred millivolts) on the ground side.
Blah, blah, blah...chasing electrical gremlins is fun, isn't it?