Thomas Neels

I bought a used 5.3ls motor. The other one blew up no oil pressure. I put a new oil pan without the relief valve in it, New pick up tube with o ring, new high volume oil pump, 5w30 oil. primed the new pump put a mechanical Guage so I could check the oil pressure at the port for the oil pressure sensor which i put a new screen in there as well. Still no oil pressure until I fired it up and reverse it up to 3000rpm then got 20psi but when let off the gas it drops to 0. I have been dealing with this issue for 4 months and we desperately need our tahoe back. Any suggestions would be appreciated. Thought about draining the oil for the 7th time and maybe putting in a thicker oil. I just need to figure out how to get oil pressure to the top of the motor. Also if I take my mechanical Guage off and turn it over oil does shoot out the top but I dint know why I can't get oil pressure it's got me stumped PLEASE HELP I have alot of money invested in this to blow it up again.