Ok so let me give you y usual preface of I'm no mechanic, and not mechanically inclined but I do know the bare basics a man should know.
Ok the problem arose last week around Thursday on my load home. I noticed my voltmeter said 12.8 or so rather my usual 13.6 to 14.1 or so. Parked it next day for the weekend, went to crank Monday afternoon to get my next load, it hesitated and made its noises slowly before starting. Voltmeter at around 12.5 or so now. Drive it to get fuel and it's at 12 now, maybe 11.9 because light came on. At this point I checked the alternator with multimeter. It's pushing out 14.35 volts. Take steps off check batteries, all the batteries show 12.5 or so. Decide to drive to pick up see what happens. Randomly gets back up to 13.5 volts and light cuts off. Have checked alternator at least 10 times It's never less then 14. Load tester indicates all batteries are good. I changed some ugly wires and fittings, and a couple potential loose grounds I saw. It's at like 12.2 right now when earlier it was 14 when I started my day. It's a 2015 international prostar. Any ideas what I should try or look at before giving to a shop and wasting money I feel like this is something I could do with a little guidance.
Thanks in advance!