[V8] Electrical Charging Problem

[scott.olson at nokia.com]

1990 V8 Auto. 120k
A few weeks ago, Mike LaRosa wrote an excellent 'gory details' report on testing and troubleshooting the cable that runs from the battery to the alternator.   
I have been experiencing an intermittent alternator light (usually at slow speeds, and with A/C running).  So, I pulled out the tools on Sunday and went to work. 

Multimeter probes:
Car at rest.  11.9v
Car running.  13.7v
both readings taken at the front battery (-) and (+) posts and at the battery are identical, so I decided is not a corroded cable.  

What do you think is wrong?  
Alternator?  One in the car is original.... Is 120k about the life for this item?
Battery is 1.5 years old.  
Car starts quickly, no stumble.
 
Regards,
ScottO
Texas.  
Will be using A/C again by the weekend.