Electrical Issue?

I've had my truck for 3 years now and the previous owner babied it to the T. Just this past summer i was on the interstate and noticed my battery gauge slowly drop and climb back up again. Eventually it got to the last quarter of the gauge and started to sputter and died. I lost all power. I pulled over and it started right back up and i was able to get to a pep boys and they said it was the battery. Once replaced, the truck ran fine till maybe a month later when it did the exact same thing. My dad and I were stumped since the alt bench check turned out ok and no loose or bare wires were found. I took it to a mechanic and he had it for 2 days and determined the alt was giving voltage but no amperage so he swapped them out. A month has went by and everything was ok until tonight when it did the same thing. Again, it was driving fine at 60mph and battery gauge slowly dropped then it sputtered and died (lost all power). Fired right back up and acts fine now. To add to it, i did notice tonight that when I'm above 50mph and accel, the batt gauge starts to slowly drop and when i let up it goes back up.

Battery and Alt are under 2 months old and all cables seem to be ok. Any ideas or has anyone ever heard of a situation like this? Thanks ahead of your time for your input!

1998
GMC
Sonoma
2.2L
5-spd manual
93,000 Miles

Could possibly be a worn serpentine belt tensioner allowing the belt to slip. If that's the case, replace the belt too.

Another possibility is a loose or corroded connection causing excessive voltage drop. This link explains how to check it: http://www.aa1car.com/library/voltage_drop_testing.htm

Post your results.

Thanks for your reply! As I mentioned before, I took it to a local mechanic and he had it for a week and put over 100 miles on it trying to get it to do it again as well as checking other possibilities, but still no luck. Truck ran without any issues. I picked at his brain a little and went through the checklist you had posted but again, no results. Are there any other issues that could be occuring that I'm just over looking? Such as fuel related (already has new fuel filter), computer chip (wipers tend to randomly work but I've read that that's common for this model truck), or even a bad alternator that was just replaced? Made in USA of course. Thanks ahead of time for your thoughts!

i would take a close look at the pcm for loose connections, corrotion , etc...

Could be alternator, battery, or a poor connection. Just because a part is new doesn't always mean it's good. From the sounds of things, I'm not so sure your tech knows how to check for voltage drop. Along with a charging system check, that would be one of the first things to look at. Might want to find someone that specializes in electrical systems.

Battery is also a month old and just had it retested just incase. All connections that I can access are clean and tight so no worries there so far. I will take off the alternator and try to get a bench mark or even replace it if need be (it was a rebuilt but has a 5 year warranty). As for the PCM, was that a suggestion because I mentioned the wiper issue, or just a general checklist? Either way, after I further investigate I will be contacting a GM dealership to see what they have to say and if they can hook it up to a diag machine.

Did you confirm what the problem was for this electrical issue? I am having similar problems. however it just happens when I am first starting to drive off. The gauges and the radio dies for a split second or 2 and the engine seems to lose power also briefly but comes back quickly in my case.