1972 Chevy C10 350 Charging issue, everything new

[72chevyc10350]

Hi, I have recently purchased a 1972 chevy c10 with a 350. I knew the owner who put the 350 in about 10 years ago and drove it without any issues. He sold it to a friend who installed Holley Sniper EFI. He mentioned it was having some charging issues before the EFI but rarely drove it and did not trouble shoot the problem. Upon purchase I noticed the volts dropped to 10.6 upon start up. I replaced the alternator with a new 100 amp alternator. Thought the truck was fixed as it instantly showed 14.4v for the first drive after the new alternator. Next drive the truck was showing 12v and not charging appropriately. After more trouble shooting I ended up replacing almost everything in the charging system. New 2 gauge ground wire to engine, new ground wire engine to frame, bypassed voltage regulator and using new ignition hot wire with resistor and inline fuse to internally regulated 100 amp alternator, new 6 gauge alternator hot discharge to starter and existing wire started to battery. The battery is 3 years old but seemed it was constantly being drain and put on battery charger by previous owner. One a few occasion the volts on the EFI digital display would show 14.4 volts, normally after replacing something causing me to think I solved the problem but 95% of the time volts while driving are 11.8-12.3. If I let it idle for a few minutes it will slowly climb to around 13.8 but drop again while driving.

I have checked almost everything that I can think of and gone through the forums multiple times. The ignition hot wire is reading battery voltage and sending power to the alternator. Ive tried using the voltage sensing wire from the old voltage regulator for the number 2 alternator wire and also used a small jumper wire from number 2 to the alternator terminal with the same results. The EFI digital display always shows within .5v of my voltage tester.

What could cause the volts to drop so low while driving and for the charging to be irregular?

I noticed to EFI ground and hot are attached to a stud on the sidewall before going to the battery which I've heard should only go directly to the battery. Planning on fixing this next but also talked to the Holley rep who said that should cause what I am describing.

Any and all suggestions will greatly be appreciated. Thank you in advance.