Listen for the fuel pump's hum when you turn on the ignition switch. Many GM cars only run the pump for a few seconds when you turn on the ignition switch. Once the engine is running, a tap on the oil pressure sending unit takes over and sends current to the pump. If the pump doesn't run when you turn on the ignition switch, it will have to wait until oil pressure comes up during cranking. That can result in a very long crank time. This is aggravated if fuel pressure is bleeding down. It should stay up for weeks but GM has a lot of trouble with fuel pressure regulators leaking fuel into the vacuum hose on it.

Answered by caradiodoc (expert)
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