weird ignition problem on 408w

[Rhauf]

Well i have recently built a 408 stroker, and at high rpms (starting around 3,000 and getting worse as it revs higher) it seems to start dropping random cylinders or running rough. at first i thought it could be the carburetor (edelbrock 750) so i tried a holly on it, there was no change. i suspected intake valve float but a vacuum gauge showed steady vacuum at all rpms. is it possible that it could be spark plug blowout? i am really at a loss here but i hope to know before i start throwing money at ignition parts upgrades etc. so any help is appreciated! below is the specs on the engine


408w forged pistons,
10.25:1 compression,
crane roller cam 224/232 duration .540/.560 lift 112lsa,
edelbrock performer aluminum heads 2.02/1.60 valves.
weiand stealth intake
Mallory magnetic pickup distributor
"stock" coil and wires from autozone.
dual 2.5" exhaust w/ shorty headers.


now the strange thing is, i have a jet boat with a high compression olds 455 in it, and it has the same problem! (rough above 3500 rpm at any throttle/load level)