97 sub with 5.7 tbi will only start by priming tb. Once started , runs fine. Help please.

. Change fuel filter, if it hasn't been changed in 30,000 miles.

. Check fuel pressure with a mechanical gauge.

. Check fuel pressure regulator.

. Replace the Engine Coolant Temperature (ECT) Sensor ($10.99, AutoZone), which affects fuel injector pulse width. The ECT Sensor is a temperature dependent resistor (thermistor), whose resistance decreases as the engine coolant temperature increases. It provides a richer mixture when cold, leaner mixture when hot. This may be the highest probability item.

. Ensure platinum spark plugs (ACDelco only) have been changed in the last 50,000 miles.

My gut is that your fuel pressure is low, fuel injectors need cleaning, or the ECT Sensor needs replacing. Shouldn't be too hard to isolate. Put a gun to my head and I would say replace the ECT Sensor.