Bruce,
It is starting to sound to me that you are running out of cam.
Something like a "RV" type cam.Low RPM,high torque.
Have you run it without an air cleaner ? What size are you running ?
What fuel pump are you running ? Good filters ?
What ignition system are you running ? Is it getting the volts & amps it needs ?
A 428 CJ shouldn't be going flat at 4k rpm.
