I would not be surprised to find that the Aeromotive, DW, and Turbotweak pumps all come from the same factory?
All these pumps, and the Denso as well, put out more volume at 40 psi than do the Walbros and this loads up the return line so that it can become a restriction. I would not be surprised to find there is more than one version of return line employed by the factory. GM was good about using what was on the shelf at times. Chrysler was even better.
Of course, if one guy has 14.5 v at the pump and the next has 13.8, that can make a big difference as well