Truck Repair: High oil pressure on 5.9 Cummins, oil pressure gauge, brain cramp

Question
Hi, I have pieced together 5.9 engine from parts so what I have is 12 valve engine with some 24 valve parts on it like oil pump, oil cooler with relief valve and camshaft, I have used P7100 pump on it. My problem is extremely high oil pressure 150PSI + on idle. I have replaced oil filter and relief valve ( also used ) and install another oil pressure gauge on the block of the engine to verify also 150psi+. I am using 15W30 oil in it. Block is bored out 0.10 over and it has new pistons, piston rings and bearings.
I am not a mechanic or expert on Cummins but have made few engines like this before and they are still running normal, not sure what to make out of this one. Grateful in advance for any help.

Answer
The block is different for the ISB which has a hole for "dump to sump" when regulating the oil pressure.Just change the oil pump to the regular one(which needs no "upgrades").Hardly have a low oil pressure problem with the B series engine.

What parts did you swap out on the oil cooler?I had a brain cramp & the oil pump is not the problem,its the oil cooler,mounting gaskets or housing.All the above is true except the oil pump part,its in behind the oil cooler the oil pressure relief dumps back to the pan and depends on what block you have is to what cooler parts you need.