08 Silverado Voltage fluctuation

[rs74]

My father n laws 1500 started having this fluctuation issue here in the last week. I put a meter on it and it ranged from 13.2-14.8 volts. He drove it on a three hours trip and he said the the gauge was all over the place and also the other gauges and dash lights were doing different things. He replaced the battery since it was the factory one and just put a new alternator on it yesterday. Same problem this morning.

This truck has 80,000 on it and this is the first time it has happened. I have read that this is an issue with alot of these trucks but have not seen where there is a fix. Has anyone had this issue and resolved it? I have a call into the dealer ship as it has an extended warranty on it.