I'm officially ***in baffled. I borrowed an OEM alternator from a friend today, and had it bench tested before I installed it. Tested good on the bench, slapped it on the truck, and I'm seeing 12.3v at idle, bumping up 12.6v at 1500 rpm (as read off the back of the alternator with a multimeter). Everything off at that point: no A/C, no stereo, GP's finished their cycle, etc......
Double checked my voltage drop across the alternator to battery wire and read 0.17v .
Truck is real close to being parked in a public lot with a "No Lojack, no GPS, no alarm, key in the ignition. This is not a bait car" sign in the windshield.