I've seen this on an old 2000 silverado I have as work truck. Was told it was the vent tube from the tank that was plugged. We blew air into it and didn't help, but when we changed fuel pump and pressure regulator on it, it solved the issue. I still think maybe the vent tube was the issue, just didn't fully open till we pulled bed off to remove fuel pump. But guess it could be a pressure regulator issue as well, tho I think if that's the case it'll be more about the return fuel line from the fuel log where regulator is than just a pump or regulator. I'm sure this is a totally different animal, just thought maybe you can take something from that and it might help you find a place to start.