383 stroker

Hi everyone! just joined the HBB.I'm building a 69 El Camino w/ a 383 stroker.The problem is this- it runs great until 4900 rpm and then drops off completely- the dyno operator said it was getting some kind of valve float.up until that point it made 275 rear wheel horsepower on a mustang chassis dyno. he checked timing and it was 36 degrees,fuel pressure is 6psi,carb is holley 750 and was not running out of fuel,ignition checked ok.here is my setup: 383 stroker,9.5:1,speed pro hyperectic pistons,comp cams xe 268H cam-477/480 lift,1.6 roller rockers,dart pro 1 heads-64cc,edelbrock rpm air gap,holley 750,msd 6al,hei w/ 50,000 volt coil. any help would be greatly appreciated.

oops. sorry. I'll get it right next time.