i replaced the oil filter and cap with OEM parts and i still have the same issues. What is the oil pressure on the low side suppose to be? How do i test for a high pressure leak?

I replaced the oil sending unit and still have the same issue. When i went to start the engine it cranked over for 55 seconds before it started, once it starts it stays running. When the engine rpm gets below 1200 rpm the oil pressure gauge drops to zero, once i get the rpm's above 1250 rpm it...

were would i install it?

When i come to a stop, the pressure gauge drops all the way down and the check gauge light comes on. I can sit through a light and when i get the rpm's up the gauge goes up to normal. It only starts hard.

I just replaced my head gaskets, studs, injectors, glow plugs, egr delete, and oil cooler. When i wentto start the engine the first couple times it cranked forever before starting. This went away as soon as i drove it for a few miles. The other day i went to start the truck and it died...