Intermittent partial electrical failure 2003 chevy Silverado

Hello folks, have been trying to solve this for quite
a while to no avail... It all started at work when I
tried to leave. Thought that the battery was dead
which happens to be a newer Optima red top.
When I turn the key absolutely nothing happened
no solenoid no instrument cluster, nothing. Came
back to it 20 minutes later and it started fine. On
the way home that same day message flashed
across dash display saying "battery not charging"
immediately after the truck died. Started up 15
minutes later with no problems. In the last few
days problem has become more frequent. When
turning the key on no power to starter, instrument
cluster, windows, or keyless entry. Weird thing is
that headlights come on and are not dim at all.
After a while sitting in the driver's seat with the key
to the on position all of a sudden power is restored
you hear solenoid clicking and everything returns
to normal. Took it to AutoZone and battery and
alternator test were good...

Please someone help I have been late to work 3
times because of this I don't know what to do.
Every time someone takes a look at it everything
appears normal !