Ok, so not the pump(s). The irregular pressure with one of the pumps off isn't surprising... I wouldn't leave them both in place.
Personally, I'd get a wideband and a MAFT Pro, install a GM IAT and MAP sensor, delete the KVAFM and HAC altogether and then see how well you can tune it.
I'll re-read the thread later to see what we've missed or what is still suspect.
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