There are quite a bit of tricks involved in getting fuel economy as good as Duramax and Powerstroke with the CP 4 pump.
All of you may hate the CP 4 pump, but the fact is the higher pressure is necessary to simultaneously get better fuel economy and mileage.
Higher injection pressures, paired with the high tech micro nozzles in the injectors, enable a very fine, mist like spray that exposes a lot of fuel droplet surface area to oxygen in the combustion chamber.
That in turn, enable rapid combustion and reduce particulates (basically partially burnt fuel that have carbonized).
It also enables shorter bursts of injection and less fuel striking the relatively cool cylinder walls / piston top / head.
Lower pressure and slower combustion with the CP3 pump makes for bigger carbon particles.
A bigger problem is, nozzle size equal, a longer injection event to deliver the same volume of fuel in bigger droplets.
That makes it more likely that the fuel will contact the cool cylinder bore, piston top, etc. rather than fully burn.
Every bit of carbon out the tail pipe is money down the drain because it could have been oxidized to produce energy, but instead it is being captured and fuel has to burned to get rid of it.
All things equal, the Cummins have to work harder to get the same cleanness by scrubbing more particles via the DPF, and also handling a bigger volume of unburnt hydrocarbons.
That is why it is a matter of time before Cummins move to the CP4.
They may be just doing it all at once with the DEF update.
BINGO.... Plus Ford's piston design produces 50% less soot which equates to less regens as well. This also promotes improved fuel economy.