One other thing I didn't see mentioned is the solenoids have to work harder when there is 900PSI of pressure behind it. This would require more current to open the solenoids. When you tested in the garage there was no pressure in the line. I don't know if you log battery voltage either, but with the load of fuel pumps and ignition amps under heavy load will drop the battery voltage regardless of using an alternator, since you said 16V I doubt you use an alternator.