Montana with electrical issues

battery light came on while driving on x-way. then all of the panel lights started flickering. . . Van shut down. Jumped it and it went 3 blocks and died again.
Put in a new alternator . . Fixed. . . So I thought. Got on expressway for another trip. Same flickering and died. Installed new battery. Still draining battery. When I meter the alternator it shows 14+ volts for a long time. Then randomly it will start showing a drop to 12 volts and back up again. The headlights will dim and the control panel lights will flicker. I checked lines from alternator body to frame. (even installed another ground strap) checked continuity from alternator to starter to positive side of battery. All appears well but not sure what is causing my problem. If in line fuse is bad. would it meter out? can there be something telling the alternator to turn off? Like the PCM.

I would check the serpentine belt for proper tension when hot. It is possible that the belt driving the alternator is slipping when hot and causing it to decrease in efficiency. Also check the belt tensioner as it may be stuck in one spot allowing the belt to move too freely. Usually you will hear a squeal when the belt slips but not always.