Welcome to 2CarPros.
If it ran prior to the part replacement and this is the 4.3L V6, I suspect either the crankshaft position sensor was left disconnected or damaged when the work was done.
Take a look at pic 1 to locate the sensor in question. I circled it for you. Check to make sure it is fully connected and nothing was damaged.
Next, was anything other done to the vehicle? If you could, let me know the engine size.
Take care and let me know.
Joe
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Wednesday, July 3rd, 2019 AT 8:42 PM