I have recently had some problems with my 2013 Chevrolet Silverado 1500 5.3 4x4 where it will shut off all electronics and the engine and come back on right afterwards. This only happens in gear and under load from a dead stop.

Need to have a scan tool hooked up and see what it'* doing.

Also Check the battery cables to be clean & tight, with no corrosion. What is the Alternator Voltage output while it'* still running ?
How old is this battery? Get it load tested.

There are no pending or stored codes, The battery is about 4 years old I will get it tested. All grounds have been cleaned, The main ground and positive cable on the battery have been replaced, And the alternator output is 15.5-16 volts.

You need a new battery before going any further.

Yes that may be the case re the battery, as that charging voltage is a bit high indicating a weak battery.
How are you reading the output voltage? From a VOM meter or from the dash gauge (analog or digital read out?)
I'd rather see the voltage direct from a scanguage / obd2 port for more exact readings.

I checked the voltage with a voltmeter hooked right to the back of the alternator. I will have to hook the scanner up to see the voltage at the OBD2. I will get back to you afterwards

Look at system voltage while loading it up.

Voltage from obd2 port is 14.5