98 GTP won't stay running

[GTowner2016]

Bought a 98 GTP from my brother in law. He just had all gaskets in engine replaced, new injectors, water pump, recently had new fuel pump and filter. Car turns over, will briefly start then the engine jumps in the bay like it's trying to run and dies again. Any ideas? Had some people on Grand Prix group on Facebook Day to check fuel pressure and regulator as it sounded like fuel system. Could this in fact be where I need to start looking at?

 

[Scottydoggs]

do this.

 

[GTowner2016]

Discovered that the rocker arm is moving all over so we are going to pop her open and see what all damage there is.