Reprogramming required listed on that listing. EPA must have busted GM for doing a non-certified injector replacement. All calibrations and parts replacements have to be re-certified for GM to sell them as emissions compliant and the MPFI upgrade kit throws the stock programmed fueling out of the window. Probably the whole reason that kit was discontinued anyway. Rather than spend money to correct the calibrations and re-certify, cheaper to just quit making the part.
What is? Oh I see it now, Special Procedures.