Stroker Motor wont Rev pass 5200Rpm

No idea what camshaft is? Yeah that's the key piece here.

What is the idle vacuum at 750 rpm and say 16* of idle timing. Is the idle really smooth or is it a choppy cammed up idle.

I bet it has a small cam in it and runs out of steam early that is exacerbated by the larger CI stroker.

Just a WAG based on limited information.

Ha you actual live pretty close to me...