Ok, another little test to do to make sure it is not a engine oil pump issue, thes trucks have 2 oil pumps and if the engine oil pump isn't working then the high pressure pump won;t have the oil to work.
You can pull the oil filter cap off and hold the plunger down and crank it over to see if housing fills with oil

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You do have a stock cap Right?? not one from Napa that has the filter attached to cap, they are known for not holding the plunger down properly and causing low oil presure.

 

yes sir.stock oil cap

 

what did u find wrong with your truck I'm going through the exact same thing

 

$100 says it was the FICM. I had all these same issues with mine recently and it turned out to be the FICM. Usually the power side goes bad in them but on mine it was the logic side that went. So even tho doing the voltage test showed proper voltage, it still wasnt communicating with the pcm. Probably cost me close to $2k by the time i was finished messing around but at least it runs. Still have a possible vgt solenoid issue and possibly oil rail seals or injector seals but its running...thats a start.