chad rock

I built a 383 that falls off 20 hp @ 5800 then goes flat till 6400 .It made412hp sae @ 5400 and 413 ft lbs @4500 .ls6intake stock ptb,stock 99 model pds maf,fl headers,10.9 to 1 comp,new patriot stage2 225 2.05 and 1.60s,228 230@50 with 579 595 lift ,and stock rockers.afr is good throughout the curve. same cam with stock heads in 346 with ls1 intake pulled to 6400.I really feal it should be making more power or at least not have the small drop off at 5800 . those numbers were through a cut out bye the way .input on this matter would be greatly appreciated thanks