When you say at the same condition do you mean when I’m experiencing the voltage drop? Which is while the car is in drive and I’m stopped?

 

Same engine speed, same electrical load.

You can do it when things are fine, you can do it when things are misbehaving. And then compare results.

 

In posts #29 and #36 I have those readings

 

Let's get wild and crazy and make up a 10ga piece of wire and connect it from the battery to the alternator and go for a spin and see what happens. Of course I'm assuming that each and every other connection of both ends of the battery cables is bright and tight. Also assuming that the grounds are all good, electricity has to go home.

 

Isn’t the wire that runs from the battery to the alternator already a 10 gauge?

 

Yes, but it could be bad.
Personally, I think your alternator is not able to put out at low (idle) RPM...