motor knock at cold startup ... for about 1.5 seconds ??

While it knocks for that second , there is no oil pressure reading. Goes right away and the pressure jumps up to above 50 lbs.. Truck runs excellent .

Doe's it sound like a hydraulic lifter, that might leak down over night?

Change oil, and try some lucas oil treatment.

ahhh .... It is in my opinion a lower end knock , probably Rod . I am bleeding oil pressure pretty quickly .... bout 20 minutes after shutdown. Oil pressure appx.. 18 lbs. warm @ idle , 57-60 cold @ idle . Obviously I am hoping it is something other than a clearance issue... was thinking possibly oil pump bleedoff ??? Looking for some advice from past experience , before I open her up . Thanx

ahhh .... It is in my opinion a lower end knock , probably Rod . I am bleeding oil pressure pretty quickly .... bout 20 minutes after shutdown. Oil pressure appx.. 18 lbs. warm @ idle , 57-60 cold @ idle . Obviously I am hoping it is something other than a clearance issue... was thinking possibly oil pump bleedoff ??? Looking for some advice from past experience , before I open her up . Thanx

what oil do you use ? who made it ? what brand oil filters ? how long between oil changes ?

Piston slap is pretty normal in these....if it is a 5.7. You didn't really specify an engine size. Mine has been doing it every winter for the past 8 years (as long as I have owned it). It sounds like a heavy knock, just like a lower end noise. The truck now was 197 thousand miles on it. I get about 60 lbs of oil pressure cold and about 45 lbs when warm and idling. I'm really not worried about it since it goes away after a few minutes of warm up. I have also had problems with Fram filters, they bleed down quickly. If I use an AC or Purolator, the anti drain back valves on the filters work better.

I use garbage , garbage , and garbage ....... will try better L-O-F products . It is a 5.7 , and it goes right away ..... 1 second . I don't think Piston slap would go away in a second ?? ahh ..... hopefully lousy oilfilter . I will change Lube products and give an update . 99 Tahoe 5.7 , driven 100 miles a nite delivering newspapers ...stop and go driving ... does not skip a beat .... oil pressure never below 20 @ idle warm .....

I use garbage , garbage , and garbage ....... will try better L-O-F products . It is a 5.7 , and it goes right away ..... 1 second . I don't think Piston slap would go away in a second ?? ahh ..... hopefully lousy oilfilter . I will change Lube products and give an update . 99 Tahoe 5.7 , driven 100 miles a nite delivering newspapers ...stop and go driving ... does not skip a beat .... oil pressure never below 20 @ idle warm .....

with engine wear getting out of normal range engine slaps/lifter noises are to be expected on a cold worn engine.

replace the oil when at operating temp. could be oil sump screen is gunked up also.

your use is hard on the engine and transmission. replacing the transmission fluid at 20,ooomiles and the engine oil at 3,ooomiles is what this usage would require to keep things from wearing out ..

how much oil do you use every 1000miles ?