Hard to start

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last week new tune up (plugs / wires), new air and fuel filter, new fuel regulator when i turn on key fuel gauge goes to 55 psi and then drops to 0 psi, but when i turn key the rest of the way to start it starts (sometime i crank for 3 sec and stop then start cranking and it starts) then fuel pressure is 48 psi and fluxuates a little when giving it gas