Change efi or change intakes????

I'm a little surprised that the EFI system would require a strong signal like a carb venturi.

If your idle vacuum is really low because of a huge cam, it may just be outside of the "self learning" feature's parameters.

I have an MPFI setup on mine and the intake is a Super Victor which has a 3500-8000 rpm range with a carb and it's better at low RPM than the performer RPM air gap was.

I think the fuel mixing doesn't need to be done as much as with a carb since injectors spray a fine mist. So a single plane is probably fine too. But, don't think you need to change it either.