Alternator not charging?

Truck is a c4500 Kodiak. The truck has new-ish battery’s (they were tested fine) but the truck won’t charge off of the brand-new alternator. While driving the dash became dim, then the ABS light came on. Then the transmission lost reverse then the gauges went out then the sputtered for a minute and shut off. Went back about an hour later fired right up still no gauges ran for about 3 to 4 minutes then shut off again. Replaced alternator figured that's what it was started up gauges came on power probe and battery gauges started at 9 volts. Idled about 8 minutes then shut off and wouldn't start.

Bench tested the new alternator and it passed. I checked the 12v battery the junction box to the battery and it was a clean 0.1ohms, then I checked ground strap for the engine, 0.3ohms and clean. Suggestions?