Judging by the orange block with EGR block off on the head, it looks like a 360hp MP 5.7 crate engine. I see you have the TTI filter block off plate, so it's all set for the remote filter. From there, I would tend to bet on a bad oil pump. If I remember correctly, the oil pickup has a bolted flange at the oil pump and then another bolted bracket out near the pickup screen. Unless someone was careless and left those bolts out or loose, it seems likely to me that the pump went out. If the engine is the one I'm guessing above, started as a stock truck engine with a MP intake manifold and throttle body. It would have a 5.7 oil pump and a 6.1 pump would make a nice upgrade for it. Hey, it's wintertime. I'd pull the engine; check for damage; confirm why it lost pressure and upgrade the pump if that is the problem.
