I know this truck is pissing you off (Im a Mechanic also).....But you could have picked a better username
Your oil pressure is low. 14psi at hot idle is minimum. On a healthy Duramax I like to see 25psi.
What oil are you using?
Plugged oil filter?
Do a "paper towel test" on the oil. Fuel will migrate away from the oil.
◦Malfunctioning oil bypass valve
◦Oil pump worn
◦Oil pump-to-engine block bolts loose
◦Oil pump O-ring damaged or missing
◦Oil pump to oil pump tube gasket missing or damaged
◦Oil pump tube restricted or cracked
◦Oil cooler restrictions
◦Oil cooler O-rings damaged or missing
◦Excessive bearing clearances
◦Cracked, porous or restricted oil galleys
◦Oil gallery plugs missing or incorrectly installed
◦Damaged or missing oil spray cooling nozzles