I'm Neal and I am here to assist you. Only accept when you are happy with my assistance. If I can't help I will open your Question to other experts.
Why are you priming it?
Is the problem that you are not seeing pressure while cranking it over?
Ok I see, so you started it and are not getting any oil pressure?
Did you fill the oil filter with oil before instaling it?
That engine does not need to be primed, If there is no pressure then there is a problem with it.
Did you hear it run before you got it?
That was not a fresh engine so priming it was not essential, the pump is in the timing cover so it cannot be primed like the older v8s.
Was there front end damage on the truck? Was the front of the engine impacted?
No front end damage. I understand how and where the pump is/works. Not possible for all oil to have drained from sitting so long? If not oil pump what else could it be?
Are you talking about the oil pump relief valve?