Thanks Moses for replying. I received this 1998 Jeep TJ on a trade around a year ago, I was told that the motor had around 8,000 miles on it and after dissasembly it appeared to be very low mileage, due to the cross hatch on the cylinder walls was very prevalent and absolutely no ring groove at the top of the cylinder walls. The head appeared to have been freshly worked as well.
The engine gave me no problems for 4,000 miles, then while driving I noticed the oil pressure was running lower than normal between 20 to 30 lbs, (it had previously been running 40 to 50 lbs depending on rpms), Iran this lower oil pressure for around 15 min then the oil pressure dropped out to 0 the top end was rattling, I pulled over, and called a friend to bring his trailer and I trailered it home. I changed the oil pump and would have around 20 to 30 lbs until it got to operating temp and then it would drop out. The old oil pump pick up tube was in the correct location and did reach near the bottom of the sump, the new milling pump was identical of the one it replaced and as was the pick up tube.
Pulled the motor disassembled and found the main and rod bearings completely worn with copper showing full width and full circumference, the two center cam bearings were gouged in the centers full circumference, the two outer bearings showed no obvious issues.
We reused the head as it was including the push rods that were checked for straightness. We primed the new oil pump prior to installation, but did not prime the lifters.
The machine shop only vatted and removed cam bearings and did not install the new ones, they also performed the light hone.
My uncle installed the cam bearings and I assume they were installed in the correct orientation but did not see them before the cam was installed.
When we started the new motor it had immediate oil pressure between 50 to 60 lbs depending on rpms. I was planning on using a long flat head screw driver extension in my high speed drill to spin the oil pump at high revs. to see if this corrected the lifter issues.
I will definitely the oil priming you suggested, thank you for your help!! I will definitely let you know the outcome.