Current FASS products for the 7.3L and 6.0L are all HIGH PRESSURE, they have discontinued their low pressure pumps for those trucks.
The AD 100 and 150 are low pressure "helper" pumps. They give you air separation, water separation and filtration, with about 10-15psi of positive fuel pressure feeding your stock pump. This is really a great way to go as I personally believe that you get more efficient air removal at lower pump pressure, but not everyone wants to run 2 different pumps (particularly when they need more than stock volume for the main system pump like in this case). My race truck has been running an AD150 feeding a Fuelab since day one, with a 2 micron baldwin spin-on after the Fuelab.