Shouldn’t the output be around 14.2? You said one word that tells me it is probably your alternator…Duralast.
I worked at Autozone for a few months when I was around 18 and we had so many returns on parts especially alternators and starters that I really don’t know how they stayed in business. Granted that was roughly 30 years ago and they should have improved in quality, but I still don’t trust their parts.
Do your due diligence though and swap out the VR for a known good one and see what you get voltage wise. If you don’t have a spare, NAPA sells them pretty cheap.
Just my 2 cents. Keep us posted on your findings.
P.s. the original amp alternator is not going to keep up with all the additional electronics you have installed and it will overtax the alternator so that it dies an early death most likely. Consider upgrading to a 3G style at least 95 amp output. (Dash amp meter will have to be converted to volt meter and a 6 gauge wire will need to be added in addition to your original alt output wire) see the alt upgrade post on this forum: https://cccforum.discoursehosting.net/t/location-east-coast-nos-and-used-cougar-parts/67/1
Specifically the paperformance.com link on pg 2.