Voltmeter changes here and there

[Wesleycars]

I have a 2005 chevy silverado 1500 ls 4x4 with 5.3 v8 vin t and my alternator and battery went out so I replaced them, I notice that the volt meter goes from 1-2 lines after 14 then sometimes to 2-3 lines before 14. Is this normal? I do have a rockford fosgate 500w amp and a 12 kicker sub running but it does one of the two here and there. I read that it could me fuel management mode but I don't recall having that on this chevy that I know of. Thanks

[Ljmm]

Normal !

 

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[Heavy 5.7]

Wiring/resistance issue.

[bgbdwlf2500]

I would assume that the 2005 still uses the alternator that adjusts output for load. My 10 does it just from turning the headlights on and off. runs 14 with them on and a couple notches below with them off