Lights flickering getting bright/dim in line with RPM means a voltage regulation problem by definition. You want to fix something like that right away. Testing voltages on the truck is easier than alternator removal.

Alternator & Charging System Checks (Alternator Testing)

 

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Stewart

 

Could also indicate overloading. If the system is overloaded then the lights will get bright and dim with rpm as the alternator is more able to meet the load. A DC clamp on ammeter is your friend. It'll tell you right away what the alternator is putting out. Between that and a decent sized inverter plus a hair dryer you can put the system under load and do a battery of tests that is much better than anything autozone is going to do after you go to all the work of pulling it.