i have a 1970 402 BB. has less than 200 miles since rebuild. Demon 650, edelbrock performer, comp cam, Was on a cruise when started to have an issue. Loss of power, I have checked the plugs and I thought that I had located the issue....fouled plugs...problem still persists. can rev up to 2500 and she will slow to about 1500. I have checked vacuum, pvc, and timing. what else could it be?

 

Loss of power could be caused by....
Junk in the gas tank, plugged fuel filter, carb float level adjustment, wiped cam lobes, valve lash out of whack, broken pushrod(s), broken rocker arm(s), collapsed lifters, blown/leaking intake manifold, ignition shorting or overheating.
With getting fouled plugs, if you're talking about black soot and not oil fouled, then it's either running rich, or plugs are mis-firing/not firing.
Check for: distributor cap for carbon tracking, a bad coil (if engine runs fine at first, then craps out or kills), or an intake manifold gasket leaking internally (if engine runs ok at first, then craps out), or maybe even an overflowing carb.