I have an LM7 engine from a 2001 Silverado in my 300zx. After trying to build oil pressure by cranking it for 5-10 seconds on two different days with the coil packs disconnected, I observed no pressure on the cluster gauge. I then started the engine with everything connected, following advice that it wouldn't harm a well-lubricated rebuilt engine. The engine revved to 4K RPM and shut off, and the cluster gauge didn't show oil pressure. I checked and confirmed all vacuum lines were connected. Suspecting an issue with the TPS, I disconnected it. Today, I ran the engine again with an oil pressure mechanical gauge attached, and it showed 40-50 PSI. However, the engine still revved to 4K RPM and then shut off. Each time I start it, it runs for 2 seconds ramping up to 4K RPM, oil pressure shoots to 40-50 PSI, and then turns off.

I am using a 2001 GM ECM that has been tuned to remove VATs/Security for the swap. I am completely stumped on what could be causing the RPM to shoot up and then to power down. Does not seem consistent with a vacuum leak unless the ECM has some form of cut off or safety procedure that I'm not aware of (very possible).

Any help or ideas would be greatly appreciated.