jwalterus
Made in America
After driving about 3 miles and sitting 10 minutes off, it shows 12.8v on the meter .
Normal.
Your batteries are weak, your cables are bad, or your starter is shot (put a clamp meter on it to see amp draw when cranking).
Pick one, but I'd bet on the batteries, when they tested them, they should have told you "this one has *** CCA, and this one has *** CCA".
Remember, 70% of rated capacity is considered "good" on a pass/fail battery capacity test.
That's only 595 CCA on your 850 CCA battery.