Craig,
I don't have the exact gain numbers right in front of me, but our test 2003 HO trucks have seen at least 375rwhp on the dyno. The module has direct control of fuel pressure and indirect control over duration and timing.
The nice thing with our module is you are able to see how much rail pressure you are actually making. You can start at power level 1 and work your way up towards "HO" (High Output) mode and watch the fuel pressure's characteristics and decide what power levels to use in you particular situation. For example, if you want to limit your rail to 25K psi you may only be able to use 5 power levels, that choice is up to you. This makes our module great for standalone power, or ideal for fine tuning for those seeking power by stacking boxes.