Posted for Tubamanflies@aol.com:

 Larry,
 
 I don't think you are looking at a mechnical problem with the engine driven
 pump.  I had the same problem.  Good pressure that would drop off.  Boost
would
 help.  Replaced engine pump and good for a while and then same problem.
 Pulled injectors and tested flow and found air comming in from the boost pump
 seal, it was a Dukes.  Replaced boost pump, air went away and the "bad"
engine
 pump was no longer bad.
 
 Check your boost pump for seal leakage.  I bet you don't have a header tank.
 But even if you do it could still be the problem.  If you don't want to pull
 the injector lines get a long clear plastic tube and run from the engine pump
 discharge back to the tank and run the boost and look for air.
 
 I think you may find some.  Check the archive searching for "Dukes".
 
 Ray Gardner