I had a similar problem with air getting in the line. When it happen I could not get the fuel pump to prime, once I did it would run. What I had found is the new fuel sending unit has a fitting solder to the line. Well it didn't look right but I thought it was just me. I turn out the fitting had back off of the line just enough during manufacturing it had allow air between the fitting and the line. I solder it back on in it proper position and the rest is history.
Here is the thread from FetchMeAPepsi
https://6066gmcclub.com/showthread.php?t=47321&page=58