Did they switch to the Performer or the Performer RPM? Pretty big difference between the 2, regular Performer is basically an aluminum copy of the factory iron 4-bbl 360 intake but with the dual-pattern carb flange. Performer RPM is a "modern" dual-plane designed in the 1990s using Computational Fluid Dynamics (my avatar is an image of a CFD simulation of air flow through a 5.7 Hemi intake port). The RPM better damn well make more power lol.
CFD didn't exist until the 1980s or so btw, when computers started to have some actual useful power. It's literally solving hundreds of differential equations at the same time, by hand it would take years.