please help. 2007 Denali l92 6.2 has 140k a cold knock like a diesel until up to operating temp then smooth but oil pressure drops to about 10. Mechanic says new engine. Replaced sending unit but missed cleaning screen. Slight and I mean slight sense of overheat in town. No loss of power. Does not use oil and good gas mileage. Sounds like oil pump/o-ring? Not convinced piston knock because it last 10 minutes until really warm not the normal minute or less. 7000 for new crate with install or a few hundred and headache to change pump and or o ring