Can’t find anything anywhere to figure out what is wrong with my voltage.

96 4.3L V6 Chevy blazer

My issue started when I noticed I was loosing voltage on the dash gauge when accelerating. When I would idle the voltage stayed normal at 14. I went ahead and replaced the alternator with a brand new one and now when the vehicle is idle I loose voltage and when I accelerate the voltage goes back up to 14 where it should be until I’m in idle. On a cold start the voltage stays at 14 until my vehicle warms up and then it drops voltage like it’s been doing when I’m idling. So basically it seems like my alternator is giving power to the battery but the battery isn’t holding the power.

Ive asked a few people about what the issue and what it could be but they are all telling me different. They recommended either a new battery since mine is about 5 years old now, or the idle air control valve. I got the battery tested at Autozone and they said the battery tested good but I could have blown a power cell in the battery and it could just be the battery not holding a charge from the alternator.

Any help would be greatly appreciated.

 

Measure if possible with a digital multi-meter able to data-log.
I would not trust the dash voltmeter alone.
My 94 is doing the same erratic thingy on the dash (digital cluster has rather large blocks to indicate voltage). Sometimes reads less than 9 volts before starting the engine and you can tell from how it turns the engine that the battery is very good.
Then after an hours drive when I measure 13.8 volts on the digital voltmeter it says above 14 volts.

Good luck that it is just the indication.