Help, e53 problems

[E53 4.8is]

Hello everyone I'm new here. I have had my 4.8is for about 6 months now. I'm having some kind of electrical issues. During driving, my dsc light will come
On, abs, brake light. The navigation will flash on and off. The car will then studder. I'll turn it off and let it sit for 10-15 min. And it will clear codes and be good. I went in the interface were I can view voltage. With car off it's right at 12v. With it running it's all over the place. From as low as 12v to a spike as high as 15v but it's steady at 13.8-13.9 bouncing occasionally to 14.0. Is this the voltage regulator causing this havoc? Also the trans safe mode will kick in. Any ideas? I figure battery/alternator but the alternator is working fine. Now I'm guessing alternator voltage regulator. Any help is greatly appreciated. Thanks Eric.