loosing oil pressure on 1998 Chevrolet 2500 Pickup

had a 5.7 motor blew replaced it with 5.0 crate motor nothing leaks everthing look fine changed 10 of these never had a problem.normal at startup but falls quickly changed oil pump.

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1 answer
Do the oil pans and pick up tubes match with the 5.7 and 5.0? Are you verifying the loss of oil pressure with a manual oil testing gauge or are you using the dash gauge which could be off or the sending unit is bad etc? These are GM crate motors?