Low oil pressure on rebuilt engine

I just had the heads redone and just had a complete short block rebuild because of bottom end knock and low oil pressure when the engine warms up. which includes new pistons, rings, rods, bearings, valves, lifters, oil pump, and screen. The block, crank, and cam were machined. New everything else (thermostat, plugs, water pump, belts, hoses, gaskets, and seals). Also has brand new oil sending unit. The correct amount of oil showing on dipstick. Oil pump was primed. And yet I'm still showing the same low oil pressure after the truck warms up as if I didn't get any work done. I paid a lot to stop the knock in the bottom of the engine and I don't want the same issues to return! Please any advice is helpful!