Projects Fuel pump issue or something else

So my truck was running great. But it will start then die, If I hold the throttle it stay running. Let off the throttle it dies. It is a SBC 350 bored .60 over 305 heads Edelbrock cam intake and 600cfm carb. Timing set at 12 degrees at idle. I did a 40 mile round trip the other week and it ran great. Went to start it up to pull it into the garage and it dies wont idle have to feather the gas. It is a mechanical fuel pump. Fuel pressure is 4.5psi at idle. Summit fuel pump. Plugs are a nice tan color. I am thinking fuel pump.

 

If you have 4 to 5 psi it shouldn't die due to fuel starvation at idle

 

Sounds like a vacuum leak. Maybe you can spray WD 40 around the carb and intake gaskets and vacuum hoses. If the engine speeds up you have found your leak.