If THIS is how your engine sounded after start up after you noticed the Oil Pressure Gauge dropped to Zero...
Minimum Oil Pressure for the GM Atlas 4.2L Engine is 12 PSI.
In the absence of Adding Oil at regular intervals or likewise, performing Regular Oil Changes every 3,000 Miles... There are only a few circumstances that can make this catastrophic event occur:
(1) Oil Starvation and Air Cavitation caused by a COMPLETE Block Off of the Oil Pickup Tube in the Bottom of the Crank-Case caused by the occlusion from Gas Gum and Oily Carbon Solids and Engine Combustion Debris.
(2) A Separation or a Tear in the "O" Ring sealing the Oil Pick Up Tube to the Base of the Gerotor Oil Pump.
(3) The Gerotor Oil Pump Built-In Relief Valve Plunger and Spring getting STUCK or JAMMED in the Open or Relief Position on Exit of the Motor Oil into the Oil Galleries feeding the Motor right after pressurization... Essentially Dumping that Oil right back into the Crank-Case.
(4) Numbers (2) and (3) on this List can happen EVEN WITH A FULLY FILLED CRANK-CASE.
Gregory... Please... Make no attempt to Start the SUV until more information about this problem is discovered and rectified. This is hard to say, but just as
@jmonica first observed, you should NOT Start this Engine until you can have a more complete investigation performed by a competent Mechanic. If you allowed the Motor to run even for a full Minute... Serious Damage to the Crankshaft and Connecting Rods Bearings, Pistons, Rings and all (6) Cylinder Walls may have already occurred.