On these second gen trucks, the alternator has an IC unit which is integral to the alternator. The earlier trucks had an external voltage regulator, mounted near the coil.

Sounds like the IC went dead. I was able to do 4 brush swaps as the original owner of my truck before the diodes finally died.

Sounds like you are unaware that you can have the alternator tested FREE at a parts store like NAPA or Schmucks. Do that, instead of crawling under your rig to round-robin stuff.

As a consumer, 3 things you can ask them to check for you before you leave the parts store:
Battery--load/cell test
Alternator
Starters
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You might not have a spare alternator, but at least you'll have yourself a core return up front later on. Check it out.