2007 4.7l Sequoia Alternator Issue

Hi, I have what seems to be a plain old alternator not charging issue where the car will start and run connected to battery but if you disconnect the battery the engine dies immediately. In the past I had a scenario where the charging voltage gauges in cabin never moved off 9v(bottom rest) like the alterator wasnt charging but an hour later, it was showing 13 vdc plus while running like something intermittent. THe other day the truck seemed to run off of battery only and the guages were flashing on and then off (oil, charging, fuel, all of them) frequently.

The battery was pretty low voltage and once charged, the truck ran again ok but disconnecting the battery caused the engine to die. In the past this would not cause the engine to die.

The battery cables at the battery and at the alternator seemed to be pretty tight and doesnt appear to be any corrosion.

Checked all the fuses and they look ok.

what am I missing?