Whats the cam duration at .050?
Did you use lifters and springs made for this cam or stock. It sounds like you should eaisly hit 5600.
Have you tried to move the rev limiter up to higher rpm or take it off and see if it still wont rev.
Does it just flatten out or does it studder out like rev limiter. Also do you have a soft rev limiter. Some will hold the engine at certain rpm without the poping and shutter of old style rev limiters.