P1sc procharger. Shorty headers, That's basically it haha running 10:1 compression, about 7 psi at the manifold. I made 422hp 398tq at 5800 rpm (maxed my maf)
Figured something was wrong....you have 1K RPM's left dude...
Get a new MAF or Diablo...suspect you should be about 450RWHP.
Most Bolt-on 5.0 make 410 to 425 RWHP from what I hear depending on mods