Well-titled post. Sounds only too familiar.

Have you checked your exhaust for leaks? Even a small leak can throw off the
O2 sensor reading, more noticeably at idle than under load.

Another list member writes that adding grounds can CREATE running problems.
I did the same thing you did to my van, built a "ground web," and though I
don't understand the electronic theory behind it, am thinking about removing
mine. According to this theory, grounds should all come to one particular
point, and anything else detracts from the effectiveness of the grounds.

It sounds like you're on top of things, but I know my van runs lousy when
the thermostat is sticking open.

Geza