Ignoramus22470 wrote:

A followup. Very embarrassing and very typical.

What was wrong was that I mixed up the supply and return lines, so the
fuel pump was pumping into the return line.

The truck now runs great and I have a foot in my mouth.

Oh, GOSH! Well, when working with unfamiliar equipment with
multiple hoses, it is easy to have something like this happen.
That would certainly foul up the regulator function and explain
why the spring worked opposite of how it should. Take the
foot out, you DID find and fix the problem, it just took a little
bit longer!

Jon