Already replaced the Battery. Basically the truck went bat crazy on my son recently and all the lights and error codes came on.

Now, that battery light comes and goes sporadically.

I checked voltage when running and it is steady around 13.5 and 13.6. When I first start it, it immediately goes up to 14.1 but then after a few seconds it rolls back down to 13.5 and 13.6

Just want a vetted sanity check before I go buy a new alternator.

 

The running voltage seems a touch low. But its very temperature dependent. Have you cleaned the negative ground at body? Have you inspected the large fusable link for corrosion that sits inside the black plastic box on the positive lead? I had these issues once, but never bad enough for the battery light to come on.

 

did not check the negative at the body. Will check that when I get my hands back on it.

 

Not sure about mileage, but the good thing is that changing the alternator is a great preventative measure.

 

Whats the best bet on buying a alternator. British Atlantic wants $400

Is there a OE.

I've heard some say that the alternator they bought from Autozone/advance over charged and blew the electronics on their truck. Could be urban myth.

 

Denso is OE. They run around $300 at the wholesalers. Might try LK8.

 

I've had good luck with a re-manufactured by AC Delco unit sourced from Rock Auto. It was the only re-manufactured unit i could find that all bushings, bearings and brushes are replaced with new ones. 24 month warranty.
Most "rebuilt" ones these days seemed to be cleaned, tested and all the gets replaced is what has failed.
If you can find a new Denso for $300 that would also be a good option...

 

255 BP, which is about 327 US shipped at Advanced Factors website , new Denso unit.

 

Another option to consider is finding someone local to rebuild. I just went that route with my alternator, although the place I went couldn't find one of the parts and ended up getting me a reman from one of their suppliers.