What year is your truck?
Secondly it is not needed for the stock pulley. It itself does not increase power.
IF you have a TRD s/c, '09+, reflash and no intent to wire in an aftermarket ECU, then if you want to add a little more boost without maxing out your injectors, then you need to do the FPR mod. Thus increasing fuel pressure, increasing the effective flow rate of the injectors, and giving you a little more HP potential with the 425's than if they stayed at static pressure.
Ah, I think I get it now. I have an 07 with the reflash. Planning on going with the 2.85 pulley.