Let me do some out loud thinking here.
Is it possible that while the tank is negatively pressurized, that once the truck is shut off that is could drain the fuel out of the injection pump and fuel lines?
Not unless you have a hole in your line. The vacuum is pulling on both lines equally.
And regardless of what happens in the line, it cannot affect the IP, as it's on the other side of the fuel solenoid.


..must have been going down hill--a STEEP hill!......
...