I'd be surprised if the symptoms were related. Coincidence, correlation, and
causation are often confused. Post hoc, ergo propter hoc, and all that.  But
who knows.

Does the voltage off the O2 sensor vary when the engine is fully warmed up?
It should swing back and forth around .5 vdc. If it doesn't, the first thing
I'd check is the green coaxial cable where the sensor connects to the ECU.
The copper ground sheathing sometimes gets in contact with the wire coming
from the sensor, leading to crappy running conditions like you describe, and
low voltage (because it's grounding out.) Check that first--hey, it's
free--because if that connection is bad, nothing you do will make the van
run right.

O2 sensors themselves usually aren't the source of running problems.

Once you've made sure that infamous green wire is good, look for vacuum
leaks. Also, do the ECU pin test described in Bentley--it's easy, and again,
free.

Check your charging voltage at the battery with the engine running. If it's
less than 13 volts, you have some kind of a problem in your charging system.
Again, doing the free stuff first, resolder the connectors at the
alternator, and clean and retighten  the connectors at the starter. That
might solve the alt light problem. Assuming your new alternator is good.