Get that cutout installed and a tune and you will be there. That Chokemaster actually flows worse than a stock muffler. And you didnt mention a tune on there at all. The stock PCM can compensate only so much, a tune will wake it up nicely. And just pick up a set of cheap LT4 valvesprings from Jegs for $39 to replace your tired stock ones.
94 Z28 M6 hardtop power nothing LS1 lid, ported MAF, Pacesetter LT's, ORY, dump, 7/16 NSA Pro Mags, CSR EWP, Bilstein HDs, BMR springs, 32 front 23 rear sway bars, MSD opti, NGK TR55s, Taylor 8.2mm, B&M ripper shifter, underdrive pulley, Trifecta tune, LT4 KM, Poly LCAs and short TA, 3.73s, 295/35/18s