2000 Silverado low oil pressure

[Logan Anthony]

2000 chevy Silverado 1500 5.3, has low oil pressure problems, my mechanic and I have replaced the oil pressure sending unit, it now has a milling high flow oil pump, thoroughly cleaned pickup tube, cleaned oil pan, and have ran diesel thru it to clean the engine and then did sea foam to clean the engine. When cold has 30 psi, when warm has 20 psi while driving and 0psi when stopped or in park, also once warmed up and it hits zero a lifter tick starts getting louder. I’m just looking for last minute things to try before getting a new motor, thanks in advance for the help! Oh by the way the truck has 272k miles on the odo