GMC Repair: oil pressure,,, excessive oil consumption, low oil pressure

Question
QUESTION: have 2005 5.3 sierra z71, i have an oil pressure issue,,my oil pressure varies jumps up to the normal 40 then it will sometims fall below 20 but stays pretty  much between 25 and 35lbs...and when it drops i here a lifter noise,, loud noise,,and when i shut the engine off for a few seconds and then turn it back on it the oil pressure is fine,,,for awhile,,,and i was told by a GMC dealer that when they removed the pcv valve and replaced it with a baffle,, that it has been an issue in causeing fluxations in the oil pressure when they get clogged up.  i was told that gmc re designed the valve covers with the baffle to correct this problem is this true...

ANSWER: I have found an internal bulletin only available to us here at GM dealers, its number is
PIP4492K: Excessive Oil Consumption And/Or Blue Exhaust Smoke - Possible PCV Baffle Or Lifter - (Feb 1, 2010

But it deals more with oil consumption and possible leak, not so much oil pressure, I see no active documents from GM regarding oil pressure issues with your vehicle.  First and foremost has the oil been changed at the appropriate intervals  3,000-5,000 miles?  If so you should not have an issue with oil sludge in the oil pan.  If not or unsure you may have a sludge condition where the oil pump screen is blocked.

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QUESTION: the oil is changed every 3,000 miles,,, first,, no thinks it could be the oil pump,, because the pressure varies,,,
2nd,, can the screen be cleaned,or do you have to replace the oil pump,,
3rd,, i lose a little oil consumption about a quarter to half a quart,,between oil changes.
when the pressure drops below 20 i do get a knocking noise,,on the right side,,
also when starting the truck,, after sitting all night,,i get low oil pressure warning for about 3seconds and goes away...
i have been told possibly cracked head,,because about a 10 months ago,,i had some coolant loss,, and no one could find where it was disappearing too and then it stopped. lhave pressure checks done,, appears to be no leak in the radiator or the head,, i am at a loss,,
my local Gmc dealer is convinced it is this valve cover baffle problem,,he states that gmc hasnt had and they havent had to replace a hand full of oil pumps in the last 5 years,,ive been told this by several mechanics and dealers.  any suggestions,, thank you

Answer
the oil you are consuming is well below the normal amount listed by GM of 1 quart per 1,0000 miles, as for the coolant loss, could have been a slight leak in the intake whereas coolant blew out through the EGR which you are not going to see without taking the intake off.  Assuming you still have Dex-cool in the truck it may have sealed itself as that is the intent of dex-cool.  You can clean the screen for the oil pump by removing the oil pan, however at that point you might as well put an oil pump in it at that point.  Cheaper option to rule out the pump would be the valve cover, but as you stated we have not seen that many either.  Last ditch here is, the PCV that you have in the truck, is it GM or aftermarket.  We have had many aftermarket ones that caused mulitple issues.