1999 Chevy Tahoe engine will not start unless sprayed with

Sounds like a weak fuel pump. Need to get agauge to verify this, the schrader valve is on the fuel rail. Should be between 60-66 psi for the 5.7 L engine and between 55-62 psi for the 5.3 L engine. Even if they come up to pressure, shut key off and see how fast they bleed off, another sign of a bad pump. If ypu do replace the pump I highly suggest using an A/C Delco pump, they cost more but are better pumps

Lets try a little experiment. Under the hood on the driver's side is a single connector on a red wire sticking out of the wire harness. Before you start the engine cold, feed this connector with 12 volts for a few seconds. You should hear the fuel pump run. Then, try to start the truck and see what happens. Let me know. I'm suspicious of your fuel pump relay or fuel pressure regulator.