I have a 19 6.2L NHT with 53,000 miles alternator started squeaking, sounded like your typical idler pulley failure. Just a few notes for others:
You will need a T-25 torx to remove passenger side cooling fan to remove the long bolt (passenger side bolt)
also get belts from GM... (now there are 2)
Both are “Stretch Belts”
The A/C compressor belt came with the tool for install, the serpentine did not.
Remove lower front plastic skid plate it makes it easier to turn the engine over with a breaker bar or long 1/2” drive... hope this helps.